Positive resist composition and method of forming resist pattern

ABSTRACT

A positive resist composition including a resin component (A) which exhibits increased alkali solubility under action of acid and an acid-generator component (B) which generates acid upon exposure, the resin component (A) including: a polymer (A1) including a structural unit (a0) represented by general formula (a0) shown below and no structural unit (a1) derived from an acrylate ester containing an acetal-type acid dissociable, dissolution inhibiting group, exclusive of the structural unit (a0), and a polymer (A2) including the structural unit (a1) and no structural unit (a0).

RELATED APPLICATIONS

This application is the U.S. National Phase filing under 35 U.S.C. §371 of PCT/JP2007/060242, filed May 18, 2007, which designated the United States and was published in a language other than English, which claims priority under 35 U.S.C. §119(a)-(d) to Japanese Patent Application No. 2006-172554, filed Jun. 22, 2006. The contents of these applications are incorporated herein by reference in their entireties.

TECHNICAL FIELD

The present invention relates to a positive resist composition and a method of forming a resist pattern.

BACKGROUND ART

In lithography techniques, for example, a resist film composed of a resist material is formed on a substrate, and the resist film is subjected to selective exposure of radial rays such as light or electron beam through a mask having a predetermined pattern, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film. A resist material in which the exposed portions become soluble in a developing solution is called a positive-type, and a resist material in which the exposed portions become insoluble in a developing solution is called a negative-type.

In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have led to rapid progress in the field of pattern miniaturization.

Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are now starting to be introduced in mass production of semiconductor elements. Furthermore, research is also being conducted into lithography techniques that use an exposure light source having a wavelength shorter than these excimer lasers, such as F₂ excimer lasers, electron beam, extreme ultraviolet radiation (EUV), and X ray.

Resist materials for use with these types of exposure light sources require lithography properties such as a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity to these types of exposure light sources. As a resist material which satisfies these conditions, a chemically amplified resist is used, which includes a base resin that exhibits a changed alkali solubility under action of acid and an acid generator that generates acid upon exposure.

The reaction scheme of a chemically amplified resist is as follows. Upon exposure, acid is generated from the acid generator, and the alkali solubility of the base resin is changed by the action of the generated acid. For example, a positive-type resist typically contains, as a base resin, a resin having acid dissociable, dissolution inhibiting groups which dissociate by action of acid generated from the acid generator. When acid acts on such a resin, the acid dissociable, dissolution inhibiting groups dissociate, and the alkali solubility of the resin is increased.

Generally, when a resist pattern is formed using a chemically amplified resist, a baking treatment (post exposure baking; hereafter, abbreviated as “PEB”) is conducted. By conducting PEB, diffusion of acid within the resist film and dissociation of the acid dissociable, dissolution inhibiting groups are promoted. As a result, a chemically amplified resist is capable of achieving an extremely high sensitivity, as compared to a conventional non-chemically amplified resist.

Currently, chemically amplified resins that contain structural units derived from (meth)acrylate esters within the main chain (acrylic resins) are widely used as base resins for resists that use ArF excimer laser lithography, as they exhibit excellent transparency in the vicinity of 193 nm (for example, see Patent Document 1). Further, as such acrylic resins, those which have a structural unit derived from (meth)acrylate ester having an aliphatic polycyclic group such as an adamantane skeleton at the ester portion are generally used, as they exhibit excellent transparency in the vicinity of 193 nm and excellent dry-etching resistance.

Further, for improving the lithography properties, those which have plurality of structural units are currently used as the base resin component of chemically amplified resists. For example, a positive resist has a structural unit containing an acid dissociable, dissolution inhibiting group which is dissociable under action of acid generated from the acid generator, and also has a structural unit containing a polar group such as a hydroxyl group, a structural unit containing a lactone structure, and the like. Especially, a structural unit containing a polar group is widely used, as it enhances the affinity of the resist for an alkali developing solution, and contributes to improvement in the resolution. For example, in an acrylic resin, a (meth)acrylate ester having a hydroxyl group-containing aliphatic polycyclic group at the ester portion, such as a structural unit derived from hydroxyadamantyl (meth)acrylate, is generally used.

Here, the term “(meth)acrylic acid” is a generic term that includes either or both of acrylic acid having a hydrogen atom bonded to the α-position and methacrylic acid having a methyl group bonded to the α-position. The term “(meth)acrylate ester” is a generic term that includes either or both of the acrylate ester having a hydrogen atom bonded to the α-position and the methacrylate ester having a methyl group bonded to the α-position. The term “(meth)acrylate” is a generic term that includes either or both of the acrylate having a hydrogen atom bonded to the α-position and the methacrylate having a methyl group bonded to the α-position.

[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2003-241385

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

However, since the above-mentioned base resins have a polar group such as a hydroxyl group, such base resins had a problem in that they exhibit poor solubility in an organic solvent. Such poor solubility of the base resin in an organic solvent causes disadvantages such as labor and time in preparation of a resist solution, low stability of the resist solution prepared, and the like. Further, problems are caused in the synthesis of the base resin. For example, when synthesis of a resin is conducted using a monomer exhibiting high polarity, such as the aforementioned hydroxyadamantyl (meth)acrylate, the viscosity of the generated polymer becomes higher as the amount of the monomer added is increased, and hence, it becomes difficult to purify the generated polymer. Therefore, there is a large limitation in the amount of the monomer exhibiting high polarity, such as hydroxyadamantyl (meth)acrylate.

For avoiding the aforementioned problems, the use of a resin which does not have a structural unit containing a polar group has been considered. However, when such a resin is used, various lithography properties such as sensitivity, resolution and pattern shape are deteriorated. Therefore, in recent years, as requirements for improvement in lithography properties increase, it has been difficult to improve the solubility of a base resin in an organic solvent.

In recent years, one of the lithography properties which is required to be improved is the PEB margin. The PEB margin describes a property wherein a resist pattern having a target size can be stably formed independently of any variations in temperature during the PEB treatment conducted during formation of the resist pattern. An excellent PEB margin is advantageous in that fluctuation in the size of the resist pattern formed is unlikely to occur, even when the bake temperature differ depending on the substrate to be used, or even when the bake temperature varies within a substrate.

However, in a conventional chemically amplified resist, when the PEB margin is improved, the shape of the resist pattern formed tend to be deteriorated, and hence, it was difficult to achieve both of improvement in the PEB margin and excellent resist pattern shape.

The present invention takes the above circumstances into consideration, with an object of providing a positive resist composition which exhibits an excellent solubility in an organic solvent, is capable of forming a resist pattern with an excellent shape, and exhibits an excellent PEB margin, and a method of forming a resist pattern.

Means to Solve the Problems

As a result of diligent studies of the present inventors, they found that the above-mentioned problems can be solved by combining two specific polymers. The present invention has been completed, based on this finding.

Specifically, a first aspect of the present invention is a positive resist composition including a resin component (A) which exhibits increased alkali solubility under action of acid and an acid-generator component (B) which generates acid upon exposure,

the resin component (A) comprising:

a polymer (A1) including a structural unit (a0) represented by general formula (a0) shown below and no structural unit (a1) derived from an acrylate ester containing an acetal-type acid dissociable, dissolution inhibiting group, exclusive of the structural unit (a0), and

a polymer (A2) including the structural unit (a1) and no structural unit (a0).

wherein R represents a hydrogen atom, a halogen atom, a lower alkyl group or a halogenated lower alkyl group; Y¹ represents an aliphatic cyclic group; Z represents a tertiary alkyl group-containing group or an alkoxyalkyl group; a represents an integer of 1 to 3, and b represents an integer of 0 to 2, with the proviso that a+b=1 to 3; and each of c, d and e independently represents an integer of 0 to 3.

Further, a second aspect of the present invention is a method of forming a resist pattern, including: applying a positive resist composition of the first aspect to a substrate to form a resist film on the substrate; conducting exposure of the resist film; and developing the resist film to form a resist pattern.

In the present description and claims, the term “structural unit” refers to a monomer unit that contributes to the formation of a resin (polymer).

An “alkyl group” includes linear, branched or cyclic, monovalent saturated hydrocarbon, unless otherwise specified.

The term “alkylene group” includes linear, branched or cyclic divalent saturated hydrocarbon, unless otherwise specified.

A “lower alkyl group” is an alkyl group of 1 to 5 carbon atoms.

The term “exposure” is used as a general concept that includes irradiation with any form of radiation.

EFFECT OF THE INVENTION

According to the present invention, there are provided a positive resist composition which exhibits an excellent solubility in an organic solvent, is capable of forming a resist pattern with an excellent shape, and exhibits an excellent PEB margin, and a method of forming a resist pattern.

BEST MODE FOR CARRYING OUT THE INVENTION

<<Positive Resist Composition>>

The resist composition of the present invention includes a resin component (A) (hereafter, referred to as “component (A)”) which exhibits increased solubility in an alkali developing solution under action of acid and an acid-generator component (B) (hereafter, referred to as “component (B)”) which generates acid upon irradiation.

In the positive resist composition, the component (A) is alkali insoluble prior to exposure, and when acid is generated from the component (B) upon exposure, the generated acid acts on the component (A) to increase the alkali solubility thereof. Therefore, in the formation of a resist pattern, by conducting selective exposure of a resist film obtained by using the positive resist composition, the exposed portions become alkali soluble, whereas the unexposed portions remain alkali insoluble, and hence, a resist pattern can be formed by alkali developing.

<Component (A)>

In the present invention, the component (A) includes a polymer (A1) including a structural unit (a0) represented by general formula (a0) shown below and no structural unit (a1) derived from an acrylate ester containing an acetal-type acid dissociable, dissolution inhibiting group, exclusive of the structural unit (a0), and a polymer (A2) including the structural unit (a1) and no structural unit (a0).

In the present description and claims, the term “structural unit derived from an acrylate ester” refers to a structural unit which is formed by the cleavage of the ethylenic double bond of an acrylate ester.

The term “acrylate ester” is a generic term that includes acrylate esters having a hydrogen atom bonded to the carbon atom on the α-position, and acrylate esters having a substituent (an atom other than a hydrogen atom or a group) bonded to the carbon atom on the α-position, unless specified otherwise. With respect to the “structural unit derived from an acrylate ester”, the “α-position (the carbon atom on the α-position)” refers to the carbon atom having the carbonyl group bonded thereto, unless specified otherwise.

As the substituent which may be bonded to the carbon atom on the α-position (substituent at the α-position), a halogen atom, a lower alkyl group or a halogenated lower alkyl group can be mentioned.

Examples of halogen atoms for the substituent at the α-position include fluorine atoms, chlorine atoms, bromine atoms and iodine atoms, and fluorine atoms are particularly desirable.

Examples of the lower alkyl group for the substituent at the α-position include linear or branched lower alkyl groups such as a methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, pentyl group, isopentyl group, and neopentyl group.

In the present invention, it is preferable that a hydrogen atom, a halogen atom, a lower alkyl group or a halogenated lower alkyl group be bonded to the α-position of the acrylate ester, more preferably a hydrogen atom, a fluorine atom, a lower alkyl group or a fluorinated lower alkyl group. In terms of industrial availability, a hydrogen atom or a methyl group is particularly desirable.

[Structural Unit (a0)]

In general formula (a0), R represents a hydrogen atom, a halogen atom, a lower alkyl group or a halogenated lower alkyl group.

The halogen atom, lower alkyl group and halogenated lower alkyl group for R are the same as the halogen atom, lower alkyl group and halogenated lower alkyl group which may be bonded to the α-position of the aforementioned acrylate ester. As R, a hydrogen atom or a methyl group is preferable.

In general formula (a0), Y¹ represents an aliphatic cyclic group.

In the present description and claims, the term “aliphatic” is a relative concept used in relation to the term “aromatic”, and defines a group or compound that has no aromaticity. The term “aliphatic cyclic group” refers to a monocyclic group or polycyclic group that has no aromaticity.

The “aliphatic cyclic group” within the structural unit (a0) may or may not have a substituent. Examples of substituents include a lower alkyl group of 1 to 5 carbon atoms, a fluorine atom, a fluorinated lower alkyl group of 1 to 5 carbon atoms, and an oxygen atom (═O).

The basic ring of the “aliphatic cyclic group” exclusive of substituents (aliphatic ring) is not limited to be constituted from only carbon and hydrogen (not limited to hydrocarbon rings), but is preferably a hydrocarbon ring. Further, the “hydrocarbon ring” may be either saturated or unsaturated, but is preferably saturated.

The aliphatic cyclic group may be either a polycyclic group or a monocyclic group. As such aliphatic cyclic groups, groups in which two or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane which may or may not be substituted with a lower alkyl group, a fluorine atom or a fluorinated lower alkyl group, may be mentioned. Specific examples include groups in which two or more hydrogen atoms have been removed from a monocycloalkane such as cyclopentane and cyclohexane; and groups in which one or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane.

The aliphatic cyclic group within the structural unit (a0) is preferably a polycyclic group, and a group in which two or more hydrogen atoms have been removed from adamantane is particularly desirable.

In general formula (a0), Z represents a tertiary alkyl group-containing group or an alkoxyalkyl group.

In the present description and claims, the term “tertiary alkyl group” refers to an alkyl group having a tertiary carbon atom. As mentioned above, the term “alkyl group” refers to a monovalent saturated hydrocarbon group, and includes chain-like (linear or branched) alkyl groups and cyclic alkyl groups.

The term “tertiary alkyl group-containing group” refers to a group which includes a tertiary alkyl group in the structure thereof. The tertiary alkyl group-containing group may be either constituted of only a tertiary alkyl group, or constituted of a tertiary alkyl group and an atom or group other than a tertiary alkyl group.

As the “atom or group other than a tertiary alkyl group” which constitutes the tertiary alkyl group-containing group with a tertiary alkyl group, a carbonyloxy group, a carbonyl group, an alkylene group and an oxygen atom can be mentioned.

As the tertiary alkyl group-containing group for Z, a tertiary alkyl group-containing group which does not have a ring structure, and a tertiary alkyl group-containing group which has a ring structure can be mentioned.

A tertiary alkyl group-containing group which does not have a ring structure is a group which has a branched tertiary alkyl group as the tertiary alkyl group, and has no ring structure in the structure thereof.

As the branched tertiary alkyl group, for example, a group represented by general formula (I) shown below may be mentioned.

In general formula (I), each of R²¹ to R²³ independently represents a linear or branched alkyl group. The alkyl group preferably has 1 to 5 carbon atoms, more preferably 1 to 3.

Further, in the group represented by general formula (I), the total number of carbon atoms is preferably 4 to 7, more preferably 4 to 6, most preferably 4 or 5.

Specific examples of groups represented by general formula (I) include a tert-butyl group and a tert-amyl group, and a tert-butyl group is preferable.

Examples of tertiary alkyl group-containing groups which do not have a ring structure include the aforementioned branched tertiary alkyl group; a tertiary alkyl group-containing, chain-like alkyl group in which the aforementioned branched tertiary alkyl group is bonded to a linear or branched alkylene group; a tertiary alkyloxycarbonyl group which has the aforementioned branched tertiary alkyl group as the tertiary alkyl group; and a tertiary alkyloxycarbonylalkyl group which has the aforementioned branched tertiary alkyl group as the tertiary alkyl group.

As the alkylene group within the tertiary alkyl group-containing, chain-like alkyl group, an alkylene group of 1 to 5 carbon atoms is preferable, more preferably 1 to 4 carbon atoms, and still more preferably 1 or 2 carbon atoms.

As a chain-like tertiary alkyloxycarbonyl group, for example, a group represented by general formula (II) shown below can be mentioned. In general formula (II), R²¹ to R²³ are as defined for R²¹ to R²³ in general formula (I) above. As the chain-like tertiary alkyloxycarbonyl group, a tert-butyloxycarbonyl group (t-boc) or a tert-amyloxycarbonyl group is preferable.

As a chain-like tertiary alkyloxycarbonylalkyl group, for example, a group represented by general formula (III) shown below can be mentioned. In general formula (III), R²¹ to R²³ are as defined for R²¹ to R²³ in general formula (I) above. f is an integer of 1 to 3, preferably 1 or 2. As the chain-like tertiary alkyloxycarbonylalkyl group, a tert-butyloxycarbonylmethyl group or a tert-butyloxycarbonylethyl group is preferable.

Among these, as the tertiary alkyl group-containing group which does not have a ring structure, a tertiary alkyloxycarbonyl group or a tertiary alkyloxycarbonylalkyl group is preferable, more preferably a tertiary alkyloxycarbonyl group, and most preferably a tert-butyloxycarbonyl group.

A tertiary alkyl group-containing group which has a ring structure is a group which contains a tertiary carbon atom and a ring in the structure thereof.

In the tertiary alkyl group-containing group which has a ring structure, the ring structure preferably has 4 to 12 carbon atoms which constitute the ring, more preferably 5 to 10 carbon atoms, and most preferably 6 to 10 carbon atoms. As the ring structure, for example, a group in which one or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane may be mentioned. Preferable examples include groups in which one or more hydrogen atoms have been removed from a monocycloalkane such as cyclopentane and cyclohexane; and groups in which one or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane.

As the tertiary alkyl group-containing group which has a ring structure, for example, a group having the following group (1) or (2) as the tertiary alkyl group can be mentioned.

-   (1) A group in which a linear or branched alkyl group is bonded to a     carbon atom which constitutes the ring of a cyclic alkyl group     (cycloalkyl group), so that the carbon atom becomes a tertiary     carbon atom. -   (2) A group in which an alkylene group (branched alkylene group)     having a tertiary carbon atom is bonded to a carbon atom     constituting the ring of a cycloalkyl group.

In the aforementioned group (1), the linear or branched alkyl group preferably has 1 to 5 carbon atoms, more preferably 1 to 4, and most preferably 1 to 3.

Specific examples of the group (1) include a 2-methyl-2-adamantyl group, a 2-ethyl-2-adamantyl group, a 1-methyl-1-cycloalkyl group and a 1-ethyl-1-cycloalkyl group.

In the aforementioned group (2), the cycloalkyl group having a branched alkylene group bonded thereto may have a substituent. Examples of such substituents include a fluorine atom, a fluorinated lower alkyl group of 1 to 5 carbon atoms, and an oxygen atom (═O).

As a specific example of the group (2), a group represented by chemical formula (IV) shown below may be mentioned.

In formula (IV), R²⁴ represents a cycloalkyl group which may or may not have a substituent. Examples of the substituent which the cycloalkyl group may have include a fluorine atom, a fluorinated alkyl group of 1 to 5 carbon atoms which is substituted by a fluorine atom, and an oxygen atom (═O).

Each of R²⁵ and R²⁶ independently represents a linear or branched alkyl group. As the alkyl group, the same alkyl groups as those for R²¹ to R²³ in general formula (I) above may be mentioned.

As the alkoxyalkyl group for Z, for example, a group represented by general formula (V) may be mentioned.

In formula (V), R⁴¹ represents a linear, branched or cyclic alkyl group.

When R⁴¹ is a linear or branched alkyl group, it is preferably an alkyl group of 1 to 5 carbon atoms, more preferably an ethyl group or a methyl group, and an ethyl group is particularly desirable.

When R⁴¹ is a cyclic alkyl group, it preferably has 4 to 15 carbon atoms, more preferably 4 to 12 carbon atoms, and most preferably 5 to 10 carbon atoms. Examples thereof include groups in which one or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane, which may or may not be substituted with a fluorine atom or a fluorinated lower alkyl group. Specific examples include groups in which one or more hydrogen atoms have been removed from a monocycloalkane such as cyclopentane and cyclohexane; and groups in which one or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane. Among these, a group in which one or more hydrogen atoms have been removed from adamantane is preferable.

R⁴² represents a linear or branched alkylene group. The alkylene group preferably has 1 to 5 carbon atoms, more preferably 1 to 3 carbon atoms, and most preferably 1 or 2.

As the alkoxyalkyl group for Z, a group represented by general formula (VI) shown below is particularly desirable.

In formula (VI), R⁴¹ is as defined for R⁴¹ in formula (V) above, and each of R⁴³ and R⁴⁴ independently represents a linear or branched alkyl group or a hydrogen atom.

With respect to R⁴³ and R⁴⁴, the alkyl group preferably has 1 to 15 carbon atoms, and may be either linear or branched. The alkyl group for R⁴³ and R⁴⁴ is preferably an ethyl group or a methyl group, and most preferably a methyl group.

It is particularly desirable that either one of R⁴³ and R⁴⁴ be a hydrogen atom, and the other be a methyl group.

Among the above-mentioned examples, as Z, a tertiary alkyl group-containing group is preferable, more preferably a group represented by general formula (II) above, and most preferably a tert-butyloxycarbonyl group (t-boc).

In general formula (a0), a represents an integer of 1 to 3, and b represents an integer of 0 to 2, with the proviso that a+b=1 to 3.

a is preferably 1.

b is preferably 0.

a+b is preferably 1.

c represents an integer of 0 to 3, preferably 0 or 1, and more preferably 0.

d represents an integer of 0 to 3, preferably 0 or 1, and more preferably 0.

e represents an integer of 0 to 3, preferably 0 or 1, and more preferably 0.

As the structural unit (a0), a structural unit represented by general formula (a0-1) shown below is particularly desirable.

wherein R, Z, b, c, d and e are respectively as defined for R, Z, b, c, d and e in general formula (a0) above.

A monomer for deriving the structural unit (a0) can be synthesized, for example, by protecting a part or all of the hydroxyl groups within a compound represented by general formula (a0′) shown below (an acrylate ester containing an aliphatic cyclic group having 1 to 3 alcoholic hydroxyl groups) with tertiary alkyl group-containing groups by a conventional method.

wherein R, Y¹, a, b, c, d and e are respectively as defined for R, Y¹, a, b, c, d and e in general formula (a0) above.

When the structural unit (a0) has an acetal-type acid dissociable, dissolution inhibiting group, the structural unit (a0) may be regarded as a structural unit (a1). However, in the present invention, such a structural unit is included in the structural unit (a0), but not included in the structural unit (a1). That is, the structural unit represented by general formula (a0) above is not included in the structural unit (a1).

[Structural Unit (a1)]

The structural unit (a1) is a structural unit derived from an acrylate ester having an acetal-type acid dissociable, dissolution inhibiting group, exclusive of the structural unit (a0).

In the present description and claims, with respect to the acid dissociable, dissolution inhibiting group, “acid dissociable” means that the group can be dissociated from the component (A) by action of acid generated from the component (B) upon exposure. “Dissolution inhibiting group” refers to a group which exhibits an alkali-dissolution inhibiting effect to render the entire component (A) alkali insoluble prior to dissociation, and following dissociation, changes the entire component (A) to an alkali-soluble state.

An “acetal-type acid dissociable, dissolution inhibiting group” generally substitutes a hydrogen atom at the terminal of an alkali-soluble group such as a carboxy group or a hydroxyl group, so as to be bonded with an oxygen atom. When acid is generated upon exposure, the generated acid acts to break the bond between the acetal-type acid dissociable, dissolution inhibiting group and the oxygen atom to which the acetal-type acid dissociable, dissolution inhibiting group is bonded.

Examples of acetal-type acid dissociable, dissolution inhibiting groups include groups represented by general formula (p1) shown below.

wherein each of R¹′ and R²′ independently represents a hydrogen atom or a lower alkyl group; n represents an integer of 0 to 3; and Y represents a lower alkyl group or an aliphatic cyclic group.

In general formula (p1) above, n is preferably an integer of 0 to 2, more preferably 0 or 1, and most preferably 0.

As the lower alkyl group for R¹′ and R²′, the same as the lower alkyl groups for R in formula (a0) above can be mentioned. As the lower alkyl group for R¹′ and R²′, a methyl group or ethyl group is preferable, and a methyl group is particularly desirable.

In the present invention, it is preferable that at least one of R¹′ and R²′ be a hydrogen atom. That is, it is preferable that the acid dissociable, dissolution inhibiting group (p1) is a group represented by general formula (p1-1) shown below.

wherein R¹′, n and Y are as defined above.

In the present invention, a group in which R¹′ in formula (p1-1) represent a hydrogen atom is particularly desirable.

As the lower alkyl group for Y, the same as the lower alkyl groups for R in formula (a0) above can be mentioned.

As the aliphatic cyclic group for Y, any of the aliphatic monocyclic/polycyclic groups which have been proposed for conventional ArF resists and the like can be appropriately selected for use. For example, the same groups described above in connection with the “aliphatic cyclic group” can be mentioned.

As specific examples of the aliphatic cyclic group for Y, those having the structures represented by the following chemical formulas can be mentioned.

Further, as the acetal-type acid dissociable, dissolution inhibiting group, groups represented by general formula (p2) shown below can also be mentioned.

wherein R¹⁷ and R¹⁸ each independently represents a linear or branched alkyl group or a hydrogen atom; and R¹⁹ represents a linear, branched or cyclic alkyl group; or R¹⁷ and R¹⁹ each independently represents a linear or branched alkylene group, wherein the terminal of R¹⁷ may be bonded to the terminal of R¹⁹ to form a ring.

The alkyl group for R¹⁷ and R¹⁸ preferably has 1 to 15 carbon atoms, and may be either linear or branched. As the alkyl group, an ethyl group or a methyl group is preferable, and a methyl group is most preferable.

It is particularly desirable that either one of R¹⁷ and R¹⁸ be a hydrogen atom, and the other be a methyl group.

R¹⁹ represents a linear, branched or cyclic alkyl group which preferably has 1 to 15 carbon atoms, and may be any of linear, branched or cyclic.

When R¹⁹ represents a linear or branched alkyl group, it is preferably an alkyl group of 1 to 5 carbon atoms, more preferably an ethyl group or a methyl group, and most preferably an ethyl group.

When R¹⁹ represents a cycloalkyl group, it preferably has 4 to 15 carbon atoms, more preferably 4 to 12 carbon atoms, and most preferably 5 to 10 carbon atoms. As examples of the cycloalkyl group, groups in which one or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane, which may or may not be substituted with a fluorine atom or a fluorinated alkyl group, may be mentioned. Specific examples include groups in which one or more hydrogen atoms have been removed from a monocycloalkane such as cyclopentane or cyclohexane, and groups in which one or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane. Of these, a group in which one or more hydrogen atoms have been removed from adamantane is preferable.

In general formula (p2) above, R¹⁷ and R¹⁹ may each independently represent a linear or branched alkylene group (preferably an alkylene group of 1 to 5 carbon atoms), and the terminal of R¹⁹ may be bonded to the terminal of R¹⁷.

In such a case, a cyclic group is formed by R¹⁷, R¹⁹, the oxygen atom having R¹⁹ bonded thereto and the carbon atom having the oxygen atom and R¹⁷ bonded thereto. Such a cyclic group is preferably a 4 to 7-membered ring, and more preferably a 4 to 6-membered ring. Specific examples of the cyclic group include a tetrahydropyranyl group and a tetrahydrofuranyl group.

As the structural unit (a1), it is preferable to use at least one member selected from the group consisting of structural units represented by formula (a1-0-1) shown below and structural units represented by formula (a1-0-2) shown below.

wherein R represents a hydrogen atom, a halogen atom, a lower alkyl group or a halogenated lower alkyl group; and X¹ represents an acetal-type acid dissociable, dissolution inhibiting group.

wherein R represents a hydrogen atom, a halogen atom, a lower alkyl group or a halogenated lower alkyl group; X² represents an acetal-type acid dissociable, dissolution inhibiting group; and Y² represents an alkylene group or an aliphatic cyclic group.

In general formula (a1-0-1) shown above, as the halogen atom, lower alkyl group and halogenated lower alkyl group for R, the same as the halogen atom, lower alkyl group and halogenated lower alkyl group for R in general formula (a0) above can be mentioned.

X¹ is the same as the aforementioned acetal-type acid dissociable dissolution inhibiting group.

In general formula (a1-0-2), R is as defined for R in general formula (a1-0-1) above.

X² is the same as X¹ in general formula (a1-0-1).

Y² is preferably an alkylene group of 1 to 4 carbon atoms or a divalent aliphatic cyclic group. As the aliphatic cyclic group, the same as those mentioned above in connection with the explanation of “aliphatic cyclic group” can be used, except that two or more hydrogen atoms have been removed therefrom.

As the aliphatic cyclic group for Y², a group represented by general formula (y-1) shown below is particularly desirable.

wherein m represents 0 or 1.

As specific examples of the structural unit represented by general formula (a1-0-1), those represented by formulas (a1-2-1) to (a1-2-43) shown below can be mentioned.

As specific examples of the structural unit represented by general formula (a1-0-2), those represented by formulas (a1-4-1) to (a1-4-30) shown below can be mentioned.

Among the above-mentioned examples, a structural unit represented by general formula (a1-0-1) is preferable, and a structural unit represented by general formula (2) shown below is particularly desirable. By including such a structural unit represented by general formula (2), the effects of the present invention are further improved. Moreover, exposure margin, resolution and the like are also improved.

wherein R is as defined above; g represents an integer of 0 to 3; h represents an integer of 0 to 3; and R⁷⁴ represents a polar group.

In formula (2), R is as defined for R in formula (a0) above.

g is preferably an integer of 0 to 2, more preferably 0 or 1, and most preferably 0.

h is preferably 0 or 1, and most preferably 0.

As the polar group for R⁷⁴, a hydroxyl group, a cyano group, a carboxy group, a fluorinated hydroxyalkyl group which is a hydroxyalkyl group of 1 to 5 carbon atoms in which a part of the hydrogen atom(s) bonded to the carbon atom(s) are substituted with fluorine atom(s), or the like can be mentioned. Among these, a hydroxyl group or a carboxy group is preferable.

Further, R⁷⁴ is not limited to be a monovalent group, and an oxygen atom (═O; the oxygen atom forms a carbonyl group with a carbon atom constituting the ring) is also preferable. When R⁷⁴ represents an oxygen atom, h is preferably 1.

Among structural units represented by general formula (2) above, structural units represented by general formulas (3), (4) and (5) shown below are preferable, and a structural unit represented by general formula (4) is particularly desirable.

wherein R is as defined above.

{Polymer (A1)}

The polymer (A1) is a polymer including the structural unit (a0) and no structural unit (a1).

In the polymer (A1), as the structural unit (a0), one type of structural unit may be used alone, or two or more structural units may be used in combination.

In the polymer (A1), the amount of the structural unit (a0) based on the combined total of all structural units constituting the polymer (A1) is preferably 1 to 40 mol %, more preferably 1 to 25 mol %, and still more preferably 5 to 20 mol %. By making the amount of the structural unit (a0) at least as large as the lower limit of the above-mentioned range, the solubility of the polymer (A1) in an organic solvent is improved. On the other hand, by making the amount of the structural unit (a0) no more than the upper limit of the above-mentioned range, a good balance can be achieved with the other structural units.

[Structural Unit (a1′)]

The polymer (A1) preferably includes a structural unit (a1′) derived from an acrylate ester having a tertiary alkyl ester-type acid dissociable, dissolution inhibiting group, as well as the structural unit (a0).

In the present description and claims, “a tertiary alkyl ester” describes a structure in which an ester is formed by substituting the hydrogen atom of a carboxyl group with a chain-like or cyclic alkyl group having a tertiary carbon atom, and the tertiary carbon atom within the chain-like or cyclic tertiary alkyl group is bonded to the oxygen atom at the terminal of the carbonyloxy group (—C(O)—O—). In this tertiary alkyl ester, the action of acid causes cleavage of the bond between the oxygen atom and the tertiary carbon atom.

When an acid dissociable, dissolution inhibiting group is of “a tertiary alkyl ester-type”, it means that the tertiary carbon atom bonded to the terminal oxygen atom of the carbonyloxy group (—C(O)—O—) is included in the acid dissociable, dissolution inhibiting group. Generally, in such a structure, when acid is generated from the component (B), the bond between the terminal oxygen atom of the carbonyloxy group and the tertiary carbon atom is broken by the action of the acid, and the acid dissociable, dissolution inhibiting group including the tertiary carbon atom (i.e., the tertiary alkyl ester-type acid dissociable, dissolution inhibiting group) is dissociated.

As the tertiary alkyl ester-type acid dissociable, dissolution inhibiting group, any of the groups that have been proposed as tertiary alkyl ester-type acid dissociable, dissolution inhibiting groups for the base resins of chemically amplified resists can be appropriately selected for use. Generally, groups that form either a cyclic or chain-like tertiary alkyl ester by substituting the hydrogen atom of the carboxyl group of (meth)acrylic acid are widely known. The chain-like or cyclic alkyl group may have a substituent.

More specifically, examples of tertiary alkyl ester-type acid dissociable, dissolution inhibiting groups include aliphatic branched, acid dissociable, dissolution inhibiting groups and aliphatic cyclic group-containing acid dissociable, dissolution inhibiting groups.

The term “aliphatic branched” refers to a branched structure having no aromaticity.

The “aliphatic branched, acid dissociable, dissolution inhibiting group” is not limited to be constituted of only carbon and hydrogen (not limited to hydrocarbon groups), but is preferably a hydrocarbon group. Further, the “hydrocarbon group” may be either saturated or unsaturated, but is preferably saturated.

Examples of aliphatic branched, acid dissociable, dissolution inhibiting groups include tertiary alkyl groups of 4 to 8 carbon atoms, and specific examples include a tert-butyl group, tert-amyl group and tert-heptyl group.

In the “aliphatic cyclic group-containing acid dissociable, dissolution inhibiting group”, the “aliphatic cyclic group” may or may not have a substituent. Examples of substituents include a lower alkyl group of 1 to 5 carbon atoms, a fluorine atom, fluorinated lower alkyl groups of 1 to 5 carbon atoms, and an oxygen atom (═O).

The basic ring of the “aliphatic cyclic group” exclusive of substituents is not limited to be constituted from only carbon and hydrogen (not limited to hydrocarbon groups), but is preferably a hydrocarbon group. Further, the “hydrocarbon group” may be either saturated or unsaturated, but is preferably saturated.

As such aliphatic cyclic groups, groups in which one or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane which may or may not be substituted with a lower alkyl group, a fluorine atom or a fluorinated lower alkyl group, may be mentioned. Specific examples include groups in which one or more hydrogen atoms have been removed from a monocycloalkane such as cyclopentane and cyclohexane; and groups in which one or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane.

In the structural unit (a1′), the aliphatic cyclic group may be either monocyclic or polycyclic, and it is particularly desirable that the aliphatic cyclic group be monocyclic.

As the aliphatic cyclic group-containing acid dissociable, dissolution inhibiting group, for example, a group which has a tertiary carbon atom on the ring structure of the cycloalkyl group can be mentioned. Specific examples include a 1-methylcyclohexyl group, a 1-ethylcyclohexyl group, a 2-methyl-2-adamantyl group and a 2-ethyl-2-adamantyl group. Further, groups having an aliphatic cyclic group such as an adamantyl group, and a branched alkylene group having a tertiary carbon atom bonded thereto, as in the group bonded to the oxygen atom of the carbonyloxy group (—C(O)—O—) in the structural units represented by general formula (a1″) shown below, can be mentioned.

wherein R is as defined for R in general formula (a0) above, and each of R¹⁵ and R¹⁶ represents an alkyl group (which may be either linear or branched, and preferably has 1 to 5 carbon atoms).

As the structural unit (a1′), it is preferable to use at least one structural unit selected from the group consisting of a structural unit represented by general formula (a1-0-1) mentioned above in connection with the structural unit (a1) in which the acetal-type acid dissociable, dissolution inhibiting group for X¹ has been replaced with the aforementioned tertiary alkyl ester-type acid dissociable, dissolution inhibiting group, and a structural unit represented by general formula (a1-0-2) mentioned above in connection with the structural unit (a1) in which the acetal-type acid dissociable, dissolution inhibiting group for X² has been replaced with the aforementioned tertiary alkyl ester-type acid dissociable, dissolution inhibiting group.

As specific examples of the structural unit represented by general formula (a1-0-1) above in which the acetal-type acid dissociable, dissolution inhibiting group for X¹ has been replaced with the aforementioned tertiary alkyl ester-type acid dissociable, dissolution inhibiting group, formulas (a1-1-1) to (a1-1-45) shown below can be mentioned.

As specific examples of the structural unit represented by general formula (a1-0-2) above in which the acetal-type acid dissociable, dissolution inhibiting group for X² has been replaced with the aforementioned tertiary alkyl ester-type acid dissociable, dissolution inhibiting group, formulas (a1-3-1) to (a1-3-24) shown below can be mentioned.

As the structural unit (a1′), structural units represented by general formula (a1-1-01) shown below which includes the structural units represented by formulas (a1-1-1) to (a1-1-4), and structural units represented by general formula (a1-1-02) shown below which includes the structural units represented by formulas (a1-1-35) to (a1-1-41) are preferable.

In the present invention, as the structural unit (a1′), a structural unit represented by general formula (a1-1-02) is particularly desirable, as the effect of improving the PEB margin is enhanced, and the contrast (the difference in alkali solubility between the exposed portions and the unexposed portions) becomes large.

wherein R represents a hydrogen atom, a halogen atom, a lower alkyl group or a halogenated lower alkyl group; and R¹¹ represents a lower alkyl group.

wherein R represents a hydrogen atom, a halogen atom, a lower alkyl group or a halogenated lower alkyl group; R¹² represents a lower alkyl group; and h represents an integer of 1 to 3.

In general formula (a1-1-01), R is as defined for R in general formula (a0) above. The lower alkyl group for R¹¹ is the same as the lower alkyl group for R above, and is preferably a methyl group or an ethyl group.

In general formula (a1-1-02), R is as defined for R in general formula (a0) above. The lower alkyl group for R¹² is the same as the lower alkyl group for R above. R¹² is preferably a methyl group or an ethyl group, and most preferably an ethyl group. h is preferably 1 or 2, and most preferably 2.

As the structural unit (a1′), one type of structural unit may be used alone, or two or more types of structural units may be used in combination.

In the polymer (A1), the amount of the structural unit (a1′) based on the combined total of all structural units constituting the polymer (A1) is preferably 10 to 80 mol %, more preferably 20 to 70 mol %, and still more preferably 25 to 50 mol %. By making the amount of the structural unit (a1′) at least as large as the lower limit of the above-mentioned range, a pattern can be easily formed. On the other hand, by making the amount of the structural unit (a1′) no more than the upper limit of the above-mentioned range, a good balance can be achieved with the other structural units.

When the structural unit (a0) has a tertiary ester-type acid dissociable, dissolution inhibiting group, the structural unit (a0) may be regarded as a structural unit (a1′). However, in the present invention, such a structural unit is included in the structural unit (a0), but not included in the structural unit (a1′). That is, the structural unit represented by general formula (a0) above is not included in the structural unit (a1′).

[Structural Unit (a2)]

The polymer (A1) preferably includes a structural unit (a2) derived from an acrylate ester having a lactone-containing cyclic group, as well as the structural unit (a0), or the structural unit (a0) and the structural unit (a1′).

The term “lactone-containing cyclic group” refers to a cyclic group including one ring containing a —O—C(O)— structure (lactone ring). The term “lactone ring” refers to a single ring containing a —O—C(O)— structure, and this ring is counted as the first ring. A lactone-containing cyclic group in which the only ring structure is the lactone ring is referred to as a monocyclic group, and groups containing other ring structures are described as polycyclic groups regardless of the structure of the other rings.

When the component (A) is used for forming a resist film, the lactone-containing cyclic group of the structural unit (a2) is effective in improving the adhesion between the resist film and the substrate, and increasing the hydrophilicity with the developing solution.

As the structural unit (a2), there is no particular limitation, and an arbitrary structural unit may be used.

Specific examples of lactone-containing monocyclic groups include groups in which one hydrogen atom has been removed from γ-butyrolactone. Further, specific examples of lactone-containing polycyclic groups include groups in which one hydrogen atom has been removed from a lactone ring-containing bicycloalkane, tricycloalkane or tetracycloalkane.

More specifically, examples of the structural unit (a2) include structural units represented by general formulas (a2-1) to (a2-5) shown below.

wherein R represents a hydrogen atom, a halogen atom, a lower alkyl group or a halogenated lower alkyl group; R′ represents a hydrogen atom, a lower alkyl group or an alkoxy group of 1 to 5 carbon atoms; and m represents an integer of 0 or 1.

In general formulas (a2-1) to (a2-5), R is the same as R in the structural unit (a1) above.

The lower alkyl group for R′ is the same as the lower alkyl group for R in the structural unit (a1) above.

In the structural units represented by general formulas (a2-1) to (a2-5), in consideration of industrial availability, R′ is preferably a hydrogen atom.

Specific examples of structural units represented by general formulas (a2-1) to (a2-5) above are shown below.

In the structural units represented by general formulas (a2-1) to (a2-5), in consideration of industrial availability, R′ is preferably a hydrogen atom.

Of these, at least one structural unit selected from the group consisting of structural units represented by general formulas (a2-1), (a2-2) and (a2-3) is preferable. Specifically, it is preferable to use at least one structural unit selected from the group consisting of formulas (a2-1-1), (a2-1-2), (a2-2-1), (a2-2-2), (a2-3-1), (a2-3-2), (a2-3-9) and (a2-3-10).

It is particularly desirable to use a structural unit represented by general formula (a2-1) and/or a structural unit represented by general formula (a2-3), as the shape of the resist pattern formed becomes excellent.

In the polymer (A1), as the structural unit (a2), one type of structural unit may be used, or two or more types of structural units may be used in combination.

In the polymer (A1), the amount of the structural unit (a2) based on the combined total of all structural units constituting the polymer (A1) is preferably 5 to 60 mol %, more preferably 10 to 50 mol %, and still more preferably 20 to 50 mol %. By making the amount of the structural unit (a2) at least as large as the lower limit of the above-mentioned range, the effect of including the structural unit (a2) can be satisfactorily achieved. On the other hand, by making the amount of the structural unit (a2) no more than the upper limit of the above-mentioned range, a good balance can be achieved with the other structural units.

[Other Structural Units]

The polymer (A1) may also include structural units which are other than the aforementioned structural units (a0), (a1′) and (a2), as long as the effects of the present invention are not impaired. As the structural unit which is other than the above-mentioned structural units (a0), (a1′) and (a2), any other structural unit which cannot be classified as one of the above structural units, and any of the multitude of conventional structural units used within resist resins for ArF excimer lasers or KrF excimer lasers (and particularly for ArF excimer lasers) can be used, as long as the effects of the present invention are not impaired.

As such structural units, structural units (a3) and (a4) shown below can be mentioned.

[Structural Unit (a3)]

The structural unit (a3) is a structural unit derived from an acrylate ester containing a polar group-containing aliphatic hydrocarbon group, and is not included in the aforementioned structural unit (a0). The structural unit (a3) enhances the hydrophilicity of the entire component (A), and improves the compatibility of the component (A) with the developing solution. As a result, the alkali solubility of the exposed portions improves, which contributes to favorable improvements in the resolution.

Examples of the polar group include a hydroxyl group, a cyano group, a carboxyl group, or a hydroxyalkyl group in which a part of the hydrogen atoms of the alkyl group have been substituted with fluorine atoms, and a hydroxyl group is particularly desirable.

Examples of the aliphatic hydrocarbon group include linear or branched hydrocarbon groups (and preferably alkylene groups) of 1 to 10 carbon atoms, and polycyclic aliphatic hydrocarbon groups (polycyclic groups). These polycyclic groups can be selected appropriately from the multitude of groups that have been proposed for the resins of resist compositions designed for use with ArF excimer lasers. The polycyclic group preferably has 7 to 30 carbon atoms.

Of the various possibilities, structural units derived from an acrylate ester that include an aliphatic polycyclic group that contains a hydroxyl group, a cyano group, a carboxyl group or a hydroxyalkyl group in which a part of the hydrogen atoms of the alkyl group have been substituted with fluorine atoms are particularly desirable. Examples of the polycyclic groups include groups in which two or more hydrogen atoms have been removed from a bicycloalkane, tricycloalkane, tetracycloalkane or the like. Specific examples include groups in which two or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane. Of these polycyclic groups, groups in which two or more hydrogen atoms have been removed from adamantane, norbornane or tetracyclododecane are preferred industrially.

When the aliphatic hydrocarbon group within the polar group-containing aliphatic hydrocarbon group is a linear or branched hydrocarbon group of 1 to 10 carbon atoms, the structural unit (a3) is preferably a structural unit derived from a hydroxyethyl ester of acrylic acid. On the other hand, when the hydrocarbon group is a polycyclic group, structural units represented by formulas (a3-1), (a3-2), and (a3-3) shown below are preferable.

wherein R is as defined for R in general formula (a0) above; j is an integer of 1 to 3; k is an integer of 1 to 3; t′ is an integer of 1 to 3; 1 is an integer of 1 to 5; and s is an integer of 1 to 3.

In formula (a3-1), j is preferably 1 or 2, and more preferably 1. When j is 2, it is preferable that the hydroxyl groups be bonded to the 3rd and 5th positions of the adamantyl group. When j is 1, it is preferable that the hydroxyl group be bonded to the 3rd position of the adamantyl group.

j is preferably 1, and it is particularly desirable that the hydroxyl group be bonded to the 3rd position of the adamantyl group.

In formula (a3-2), k is preferably 1. The cyano group is preferably bonded to the 5th or 6th position of the norbonyl group.

In formula (a3-3), t′ is preferably 1, 1 is preferably 1 and s is preferably 1. Further, in formula (a3-3), it is preferable that a 2-norbonyl group or 3-norbonyl group be bonded to the terminal of the carboxy group of acrylic acid. The fluorinated alkyl alcohol is preferably bonded to the 5th or 6th position of the norbonyl group.

As the structural unit (a3), one type of structural unit may be used, or two or more types may be used in combination.

When the structural unit (a3) is included in the polymer (A1), the amount of structural unit (a3) based on the combined total of all structural units constituting the polymer (A1) is preferably 5 to 50 mol %, more preferably 5 to 40 mol %, and still more preferably 5 to 25 mol %.

In the structural unit (a0), when the aliphatic cyclic group for Y¹ in general formula (a0) is a hydrocarbon group, and b is 1 or 2, such a structural unit (a0) may be regarded as a structural unit (a3) in that it is a structural unit derived from an acrylate ester containing a polar group-containing aliphatic hydrocarbon group. However, in the present invention, such a structural unit is included in the structural unit (a0), but not included in the structural unit (a3). That is, the structural unit represented by general formula (a0) above is not included in the structural unit (a3).

[Structural Unit (a4)]

The structural unit (a4) is a structural unit derived from an acrylate ester containing a non-acid dissociable, aliphatic cyclic group.

Examples of the polycyclic group with the structural unit (a4) include the same groups as those described above in connection with the aforementioned structural unit (a1), and any of the multitude of conventional polycyclic groups used within the resin component of resist compositions for ArF excimer lasers or KrF excimer lasers (and particularly for ArF excimer lasers) can be used.

In consideration of industrial availability and the like, at least one polycyclic group selected from among a tricyclodecanyl group, adamantyl group, tetracyclododecanyl group, isobornyl group, and norbornyl group is particularly desirable. These polycyclic groups may be substituted with a linear or branched alkyl group of 1 to 5 carbon atoms can be mentioned.

Specific examples of the structural unit (a4) include units with structures represented by general formulas (a4-1) to (a4-5) shown below.

wherein R is as defined for R in general formula (a0) above.

When the structural unit (a4) is included in the polymer (A1), the amount of the structural unit (a4) based on the combined total of all structural units constituting the polymer (A1) is preferably 1 to 30 mol %, more preferably 10 to 20 mol %.

In the present invention, the polymer (A1) is preferably a copolymer having at least the three structural units (a0), (a1′) and (a2). Examples of such copolymers include a tertiary copolymer consisting of the aforementioned structural units (a0), (a1′) and (a2), a quaternary copolymer consisting of the aforementioned structural units (a0), (a1′), (a2) and (a3), and a quaternary copolymer consisting of the aforementioned structural units (a0), (a1′), (a2) and (a4).

In the present invention, as the polymer (A1), a copolymer which includes the combination of three structural units represented by general formula (A-11) shown below is particularly desirable.

wherein each of R⁶¹ to R⁶³ independently represents a hydrogen atom, a halogen atom, a lower alkyl group or a halogenated lower alkyl group; R⁶⁴ represents a lower alkyl group; R²¹ to R²³ are respectively as defined for R²¹ to R²³ in general formula (I) above; and e is as defined for e in general formula (a0) above.

In formula (A-11), the halogen atom, lower alkyl group and halogenated lower alkyl group for R⁶¹ to R⁶³ are the same as the halogen atom, lower alkyl group and halogenated lower alkyl group for R above, and a hydrogen atom or a methyl group is preferable.

As the lower alkyl group for R⁶⁴, the same lower alkyl groups as those for R can be mentioned. As R⁶⁴, a methyl group or an ethyl group is preferable, and an ethyl group is particularly desirable.

As the polymer (A1), one type of polymer may be used alone, or two or more types may be used in combination.

The polymer (A1) can be obtained, for example, by a conventional radical polymerization or the like of the monomers corresponding with each of the structural units, using a radical polymerization initiator such as azobisisobutyronitrile (AIBN).

Furthermore, in the polymer (A1), by using a chain transfer agent such as HS—CH₂—CH₂—CH₂—C(CF₃)₂—OH, a —C(CF₃)₂—OH group can be introduced at the terminals of the polymer (A1). Such a copolymer having introduced a hydroxyalkyl group in which a part of the hydrogen atoms of the alkyl group are substituted with fluorine atoms is effective in reducing LWR. Such a copolymer is also effective in reducing developing defects and LER (line edge roughness: unevenness of the side walls of a line pattern).

The weight average molecular weight (Mw) (the polystyrene equivalent value determined by gel permeation chromatography) of the polymer (A1) is not particularly limited, but is preferably 2,000 to 50,000, more preferably 3,000 to 30,000, and most preferably 5,000 to 20,000. By making the weight average molecular weight no more than the upper limit of the above-mentioned range, the polymer (A1) exhibits satisfactory solubility in a resist solvent when used as a resist. On the other hand, by making the weight average molecular weight at least as large as the lower limit of the above-mentioned range, dry etching resistance and cross-sectional shape of the resist pattern becomes satisfactory.

Further, the dispersity (Mw/number average molecular weight (Mn)) is preferably 1.0 to 5.0, more preferably 1.0 to 3.0, and most preferably 1.2 to 2.5. Here, Mn is the number average molecular weight.

{Polymer (A2)}

The polymer (A2) is a polymer including the structural unit (a1) and no structural unit (a0).

In the polymer (A2), as the structural unit (a1), one type of structural unit may be used alone, or two or more structural units may be used in combination.

In the polymer (A2), the amount of the structural unit (a1) based on the combined total of all structural units constituting the polymer (A2) is preferably 10 to 80 mol %, more preferably 20 to 70 mol %, and still more preferably 25 to 50 mol %. By making the amount of the structural unit (a1) at least as large as the lower limit of the above-mentioned range, a pattern can be easily formed. On the other hand, by making the amount of the structural unit (a1) no more than the upper limit of the above-mentioned range, a good balance can be achieved with the other structural units.

[Structural Unit (a2)]

The polymer (A2) preferably includes a structural unit (a2) derived from an acrylate ester having a lactone-containing cyclic group, as well as the structural unit (a1).

As the structural unit (a2), the same structural units as those for the structural unit (a2) in the polymer (A1) can be mentioned.

In the polymer (A2), as the structural unit (a2), one type of structural unit may be used, or two or more types of structural units may be used in combination.

In the polymer (A2), the amount of the structural unit (a2) based on the combined total of all structural units constituting the polymer (A2) is preferably 5 to 60 mol %, more preferably 10 to 50 mol %, and still more preferably 20 to 50 mol %. By making the amount of the structural unit (a2) at least as large as the lower limit of the above-mentioned range, the effect of using the structural unit (a2) can be satisfactorily achieved. On the other hand, by making the amount of the structural unit (a2) no more than the upper limit of the above-mentioned range, a good balance can be achieved with the other structural units.

[Structural Unit (a3)]

The polymer (A2) may further include a structural unit (a3) derived from an acrylate ester containing a polar group-containing aliphatic hydrocarbon group, and not included in the aforementioned structural unit (a0), as well as the structural unit (a1) or the structural units (a1) and (a2).

As the structural unit (a3), the same structural units as those for the structural unit (a3) in the polymer (A1) can be mentioned.

In the polymer (A2), as the structural unit (a3), one type of structural unit may be used, or two or more types of structural units may be used in combination.

In the polymer (A2), the amount of structural unit (a3) based on the combined total of all structural units constituting the polymer (A2) is preferably 5 to 50 mol %, more preferably 5 to 40 mol %, and still more preferably 5 to 25 mol %. By making the amount of the structural unit (a3) at least as large as the lower limit of the above-mentioned range, the effect of using the structural unit (a3) can be satisfactorily achieved. On the other hand, by making the amount of the structural unit (a3) no more than the upper limit of the above-mentioned range, a good balance can be achieved with the other structural units.

[Other Structural Units]

The polymer (A2) may also include a structural unit which is other than the above-mentioned structural units (a1) to (a3), as long as the effects of the present invention are not impaired.

As such a structural unit, any other structural unit which cannot be classified as one of the above structural units (a1) to (a3) can be used without any particular limitations, and any of the multitude of conventional structural units used within resist resins for ArF excimer lasers or KrF excimer lasers (and particularly for ArF excimer lasers) can be used.

As such a structural unit, the aforementioned structural unit (a4) for the polymer (A1) can be mentioned.

When the structural unit (a4) is included in the polymer (A2), the amount of the structural unit (a4) based on the combined total of all the structural units that constitute the polymer (A2) is preferably within the range from 1 to 30 mol %, and more preferably from 10 to 20 mol %.

In the present invention, the polymer (A2) is preferably a copolymer having at least the three structural units (a1), (a2) and (a3). Examples of such copolymers include a tertiary copolymer consisting of the aforementioned structural units (a1), (a2) and (a3), and a quaternary copolymer consisting of the aforementioned structural units (a1), (a2), (a3) and (a4).

In the present invention, as the polymer (A2), a copolymer which includes the combination of three structural units represented by general formula (A-21) shown below is particularly desirable.

wherein each of R⁷¹ to R⁷³ independently represents a hydrogen atom, a halogen atom, a lower alkyl group or a halogenated lower alkyl group; and g, h and R⁷⁴ are respectively as defined for g, h and R⁷⁴ in formula (2) above.

In formula (A-21), the halogen atom, lower alkyl group and halogenated lower alkyl group for R⁷¹ to R⁷³ are the same as the halogen atom, lower alkyl group and halogenated lower alkyl group for R above, and a hydrogen atom or a methyl group is preferable.

g, h and R⁷⁴ are respectively as defined for g, h and R⁷⁴ in formula (2) above.

As the polymer (A2), one type of polymer may be used alone, or two or more types may be used in combination.

The polymer (A2) can be obtained, for example, by a conventional radical polymerization or the like of the monomers corresponding with each of the structural units, using a radical polymerization initiator such as azobisisobutyronitrile (AIBN).

Furthermore, in the polymer (A2), by using a chain transfer agent such as HS—CH₂—CH₂—CH₂—C(CF₃)₂—OH, a —C(CF₃)₂—OH group can be introduced at the terminals of the polymer (A2). Such a copolymer having introduced a hydroxyalkyl group in which a part of the hydrogen atoms of the alkyl group are substituted with fluorine atoms is effective in reducing LWR. Such a copolymer is also effective in reducing developing defects and LER (line edge roughness: unevenness of the side walls of a line pattern).

The weight average molecular weight (Mw) (the polystyrene equivalent value determined by gel permeation chromatography) of the polymer (A2) is not particularly limited, but is preferably 2,000 to 50,000, more preferably 3,000 to 30,000, and most preferably 5,000 to 20,000. By making the weight average molecular weight no more than the upper limit of the above-mentioned range, the polymer (A2) exhibits satisfactory solubility in a resist solvent when used as a resist. On the other hand, by making the weight average molecular weight at least as large as the lower limit of the above-mentioned range, dry etching resistance and cross-sectional shape of the resist pattern becomes satisfactory.

Further, the dispersity (Mw/number average molecular weight (Mn)) is preferably 1.0 to 5.0, more preferably 1.0 to 3.0, and most preferably 1.2 to 2.5. Here, Mn is the number average molecular weight.

In the component (A), the ratio (weight ratio) of the polymer (A1) to the polymer (A2) is not particularly limited. In consideration of the effects of the present invention, the weight ratio is preferably polymer (A1):polymer (A2)=90:10 to 10:90, more preferably 80:20 to 20:80, and still more preferably 75:25 to 25:75. When the ratio of the polymer (A1) is at least as large as the lower limit of the above-mentioned range, the solubility of the component (A) in an organic solvent is increased. On the other hand, when the ratio of the polymer (A1) is no more than the upper limit of the above-mentioned range, a good balance can be achieved with the polymer (A2), and the PEB margin, the shape of the resist pattern, and the like are improved.

The component (A) may contain an arbitrary resin other than the polymer (A1) and the polymer (A2), which have conventionally been proposed as a base resin for a chemically amplified resist composition. In consideration of the effects of the present invention, the total amount (% by weight) of the polymer (A1) and the polymer (A2) within the component (A) is preferably 50 to 100% by weight, more preferably 70 to 100% by weight, and most preferably 100% by weight.

<Component (B)>

As the component (B), there is no particular limitation, and any of the known acid generators used in conventional chemically amplified resist compositions can be used.

Examples of these acid generators are numerous, and include onium salt-based acid generators such as iodonium salts and sulfonium salts; oxime sulfonate-based acid generators; diazomethane-based acid generators such as bisalkyl or bisaryl sulfonyl diazomethanes and poly(bis-sulfonyl)diazomethanes; nitrobenzylsulfonate-based acid generators; iminosulfonate-based acid generators; and disulfone-based acid generators.

As an onium salt-based acid generator, for example, a compound represented by general formula (b-0) shown below can be used.

wherein R⁵¹ represents a linear, branched or cyclic alkyl group, or a linear, branched or cyclic fluorinated alkyl group; R⁵² represents a hydrogen atom, a hydroxyl group, a halogen atom, a linear or branched alkyl group, a linear or branched halogenated alkyl group, or a linear or branched alkoxy group; R⁵³ represents an aryl group which may have a substituent; and u″ represents an integer of 1 to 3.

In general formula (b-0), R⁵¹ represents a linear, branched or cyclic alkyl group, or a linear, branched or cyclic fluorinated alkyl group.

The linear or branched alkyl group preferably has 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, and most preferably 1 to 4 carbon atoms.

The cyclic alkyl group preferably has 4 to 12 carbon atoms, more preferably 5 to 10 carbon atoms, and most preferably 6 to 10 carbon atoms.

The fluorinated alkyl group preferably has 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, and most preferably 1 to 4 carbon atoms. The fluorination ratio of the fluorinated alkyl group (percentage of the number of fluorine atoms substituting the hydrogen atoms, based on the total number of all hydrogen atoms within the alkyl group) is preferably from 10 to 100%, more preferably from 50 to 100%, and it is particularly desirable that all of the hydrogen atoms are substituted with fluorine atoms, as the acid strength increases.

R⁵¹ is most preferably a linear alkyl group or a fluorinated alkyl group.

R⁵² represents a hydrogen atom, a hydroxyl group, a halogen atom, a linear or branched alkyl group, a linear or branched halogenated alkyl group, or a linear or branched alkoxy group.

Examples of the halogen atom for R⁵² include a fluorine atom, a bromine atom, a chlorine atom and an iodine atom, and a fluorine atom is preferable.

The alkyl group for R⁵² is linear or branched, and preferably has 1 to 5 carbon atoms, more preferably 1 to 4 carbon atoms, and most preferably 1 to 3 carbon atoms.

The halogenated alkyl group for R⁵² is a group in which some or all of the hydrogen atoms of the alkyl group have been substituted with halogen atoms. As the alkyl group of the halogenated alkyl group, the same as the alkyl group for R⁵² may be mentioned. As the halogen atoms for substituting the hydrogen atoms of the alkyl group, the same as the halogen atom for R⁵² may be mentioned. In the halogenated alkyl group, it is preferable that 50 to 100% of the hydrogen atoms of the alkyl group be substituted with halogen atoms, and it is more preferable that all of the hydrogen atoms are substituted with halogen atoms.

The alkoxy group for R⁵² is linear or branched, and preferably has 1 to 5 carbon atoms, more preferably 1 to 4 carbon atoms, and most preferably 1 to 3 carbon atoms.

Among these, as R⁵², a hydrogen atom is particularly desirable.

R⁵³ represents an aryl group which may have a substituent, preferably an aryl group of 6 to 20 carbon atoms, and examples of the basic ring excluding the substituent include a naphthyl group, a phenyl group and an anthracenyl group. In terms of the effects of the present invention and absorption of exposure rays such as ArF excimer laser, a phenyl group is preferable.

Examples of the substituent include a hydroxyl group and a lower alkyl group (linear or branched, and preferably has no more than 5 carbon atoms, and a methyl group is particularly desirable).

As the aryl group for R⁵³, those which do not have a substituent are preferable.

u″ is an integer of 1 to 3, preferably 2 or 3, and it is particularly desirable that u″ be 3.

As preferable examples of acid generators represented by general formula (b-0), the following can be mentioned.

As an onium salt-based acid generator other than those represented by general formula (b-0), a compound represented by general formula (b-1) or (b-2) shown below can be mentioned.

wherein R¹″ to R³″, R⁵″ and R⁶″ each independently represents an aryl group or alkyl group; and R⁴″ represents a linear, branched or cyclic alkyl group or fluorinated alkyl group, with the proviso that at least one of R¹″ to R³″ represents an aryl group, and at least one of R⁵″ and R⁶″ represents an aryl group.

In formula (b-1), R¹″ to R³″ each independently represents an aryl group or an alkyl group. Further, among R¹″ to R³″, at least one group represents an aryl group. Among R¹″ to R³″, two or more groups are preferably aryl groups, and it is particularly desirable that all of R¹″ to R³″ are aryl groups.

The aryl group for R¹″ to R³″ is not particularly limited. For example, an aryl group having 6 to 20 carbon atoms may be used in which some or all of the hydrogen atoms of the aryl group may or may not be substituted with alkyl groups, alkoxy groups, or halogen atoms.

The aryl group is preferably an aryl group having 6 to 10 carbon atoms because it can be synthesized at a low cost. Specific examples thereof include a phenyl group and naphthyl group.

The alkyl group, with which hydrogen atoms of the aryl group may be substituted, is preferably an alkyl group having 1 to 5 carbon atoms, and most preferably a methyl group, an ethyl group, a propyl group, an n-butyl group, or a tert-butyl group.

The alkoxy group, with which hydrogen atoms of the aryl group may be substituted, is preferably an alkoxy group having 1 to 5 carbon atoms, and most preferably a methoxy group or an ethoxy group.

The halogen atom, with which hydrogen atoms of the aryl group may be substituted, is preferably a fluorine atom.

The alkyl group for R¹″ to R³″ is not particularly limited and includes, for example, a linear, branched or cyclic alkyl group having 1 to 10 carbon atoms. In terms of achieving excellent resolution, the alkyl group preferably has 1 to 5 carbon atoms. Specific examples thereof include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, an n-pentyl group, a cyclopentyl group, a hexyl group, a cyclohexyl group, a nonyl group, and a decanyl group, and a methyl group is most preferable because it is excellent in resolution and can be synthesized at a low cost.

It is preferable that each of R¹″ to R³″ is a phenyl group or a naphthyl group, and it is particularly desirable that one of R¹″ to R³″ is a phenyl group, and the other two are naphthyl groups.

R⁴″ represents a linear, branched or cyclic alkyl group or a fluorinated alkyl group.

The linear or branched alkyl group preferably has 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, and most preferably 1 to 4 carbon atoms.

The cyclic alkyl group is preferably a cyclic group, as described for R¹″, having 4 to 15 carbon atoms, more preferably 4 to 10 carbon atoms, and most preferably 6 to 10 carbon atoms.

The fluorinated alkyl group preferably has 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, and most preferably 1 to 4 carbon atoms. Further, the fluorination ratio of the fluorinated alkyl group (percentage of fluorine atoms within the alkyl group) is preferably from 10 to 100%, more preferably from 50 to 100%, and it is particularly desirable that all hydrogen atoms are substituted with fluorine atoms because the acid strength increases.

R⁴″ is most preferably a linear or cyclic alkyl group or a fluorinated alkyl group.

In formula (b-2), R⁵″ and R⁶″ each independently represents an aryl group or an alkyl group. At least one of R⁵″ and R⁶″ represents an aryl group. It is preferable that both of R⁵″ and R⁶″ represent an aryl group.

As the aryl group for R⁵″ and R⁶″, the same aryl groups as those for R¹″ to R³″ can be mentioned.

As the alkyl group for R⁵″ and R⁶″, the same alkyl groups as those for R¹″ to R³″ can be mentioned.

It is particularly desirable that both of R⁵″ and R⁶″ represents a phenyl group.

As R⁴″ in formula (b-2), the same R⁴″ as those mentioned above for R⁴″ in formula (b-1) can be mentioned.

Specific examples of suitable onium salt-based acid generators represented by formula (b-1) or (b-2) include diphenyliodonium trifluoromethanesulfonate or nonafluorobutanesulfonate; bis(4-tert-butylphenyl)iodonium trifluoromethanesulfonate or nonafluorobutanesulfonate; triphenylsulfonium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; tri(4-methylphenyl)sulfonium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; dimethyl(4-hydroxynaphthyl)sulfonium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; monophenyldimethylsulfonium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; diphenylmonomethylsulfonium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; (4-methylphenyl)diphenylsulfonium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; (4-methoxyphenyl)diphenylsulfonium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; tri(4-tert-butyl)phenylsulfonium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; diphenyl(1-(4-methoxy)naphthyl)sulfonium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; and di(1-naphthyl)phenylsulfonium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate. It is also possible to use onium salts in which the anion moiety of these onium salts are replaced by methanesulfonate, n-propanesulfonate, n-butanesulfonate, or n-octanesulfonate.

Further, onium salt-based acid generators in which the anion moiety in general formula (b-1) or (b-2) is replaced by an anion moiety represented by general formula (b-3) or (b-4) shown below (the cation moiety is the same cation as (b-1) or (b-2)) may also be used.

wherein X″ represents an alkylene group of 2 to 6 carbon atoms in which at least one hydrogen atom has been substituted with a fluorine atom; and Y″ and Z″ each independently represents an alkyl group of 1 to 10 carbon atoms in which at least one hydrogen atom has been substituted with a fluorine atom.

X″ represents a linear or branched alkylene group in which at least one hydrogen atom has been substituted with a fluorine atom, and the alkylene group has 2 to 6 carbon atoms, preferably 3 to 5 carbon atoms, and most preferably 3 carbon atoms.

Y″ and Z″ each independently represents a linear or branched alkyl group in which at least one hydrogen atom has been substituted with a fluorine atom, and the alkyl group has 1 to 10 carbon atoms, preferably 1 to 7 carbon atoms, and more preferably 1 to 3 carbon atoms.

The smaller the number of carbon atoms of the alkylene group for X″ or those of the alkyl group for Y″ and Z″ within the above-mentioned range of the number of carbon atoms, the more preferable since the solubility in a resist solvent is improved.

Further, in the alkylene group for X″ or the alkyl group for Y″ and Z″, it is preferable that the number of hydrogen atoms substituted with fluorine atoms is as large as possible because the acid strength increases and the transparency to high energy radiation of 200 nm or less or electron beam is improved. The percentage of the fluorine atoms within the alkylene group or alkyl group, i.e., the fluorination ratio is preferably from 70 to 100%, more preferably from 90 to 100%, and it is particularly desirable that the alkylene group or alkyl group be a perfluoroalkylene or perfluoroalkyl group in which all hydrogen atoms are substituted with fluorine atoms.

In the present description, an oximesulfonate-based acid generator is a compound having at least one group represented by general formula (B-1) shown below, and has a feature of generating acid by irradiation. Such oximesulfonate-based acid generators are widely used for a chemically amplified resist composition, and can be appropriately selected.

wherein R³¹ and R³² each independently represents an organic group.

The organic group for R³¹ and R³² refers to a group containing a carbon atom, and may include atoms other than carbon atoms (e.g., a hydrogen atom, an oxygen atom, a nitrogen atom, a sulfur atom, a halogen atom (such as a fluorine atom and a chlorine atom) and the like).

As the organic group for R³¹, a linear, branched, or cyclic alkyl group or aryl group is preferable. The alkyl group or the aryl group may have a substituent. The substituent is not particularly limited, and examples thereof include a fluorine atom and a linear, branched, or cyclic alkyl group having 1 to 6 carbon atoms. The expression “having a substituent” means that some or all of the hydrogen atoms of the alkyl group or the aryl group are substituted with substituents.

The alkyl group preferably has 1 to 20 carbon atoms, more preferably 1 to 10 carbon atoms, still more preferably 1 to 8 carbon atoms, still more preferably 1 to 6 carbon atoms, and most preferably 1 to 4 carbon atoms. As the alkyl group, a partially or completely halogenated alkyl group (hereinafter, sometimes referred to as a “halogenated alkyl group”) is particularly desirable. The “partially halogenated alkyl group” refers to an alkyl group in which some of the hydrogen atoms are substituted with halogen atoms, and the “completely halogenated alkyl group” refers to an alkyl group in which all of the hydrogen atoms are substituted with halogen atoms. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is particularly desirable. In other words, the halogenated alkyl group is preferably a fluorinated alkyl group.

The aryl group preferably has 4 to 20 carbon atoms, more preferably 4 to 10 carbon atoms, and most preferably 6 to 10 carbon atoms. As the aryl group, partially or completely halogenated aryl group is particularly desirable. The “partially halogenated aryl group” refers to an aryl group in which some of the hydrogen atoms are substituted with halogen atoms, and the “completely halogenated aryl group” refers to an aryl group in which all of hydrogen atoms are substituted with halogen atoms.

As R³¹, an alkyl group of 1 to 4 carbon atoms which has no substituent or a fluorinated alkyl group of 1 to 4 carbon atoms is particularly desirable.

As the organic group for R³², a linear, branched, or cyclic alkyl group, aryl group, or cyano group is preferable. Examples of the alkyl group and the aryl group for R³² are the same as those of the alkyl group and the aryl group for R³¹.

As R³², a cyano group, an alkyl group of 1 to 8 carbon atoms having no substituent or a fluorinated alkyl group of 1 to 8 carbon atoms is particularly desirable.

Preferred examples of the oxime sulfonate-based acid generator include compounds represented by general formula (B-2) or (B-3) shown below.

wherein R³³ represents a cyano group, an alkyl group having no substituent or a halogenated alkyl group; R³⁴ represents an aryl group; and R³⁵ represents an alkyl group having no substituent or a halogenated alkyl group.

wherein R³⁶ represents a cyano group, an alkyl group having no substituent or a halogenated alkyl group; R³⁷ represents a divalent or trivalent aromatic hydrocarbon group; R³⁸ represents an alkyl group having no substituent or a halogenated alkyl group; and p″ represents 2 or 3.

In general formula (B-2), the alkyl group having no substituent or the halogenated alkyl group for R³³ preferably has 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, and most preferably 1 to 6 carbon atoms.

As R³³, a halogenated alkyl group is preferable, and a fluorinated alkyl group is more preferable.

The fluorinated alkyl group for R³³ preferably has 50% or more of the hydrogen atoms thereof fluorinated, more preferably 70% or more, and still more preferably 90% or more.

Examples of the aryl group for R³⁴ include groups in which one hydrogen atom has been removed from an aromatic hydrocarbon ring, such as a phenyl group, a biphenyl group, a fluorenyl group, a naphthyl group, an anthracyl group, and a phenanthryl group, and heteroaryl groups in which some of the carbon atoms constituting the ring(s) of these groups are substituted with hetero atoms such as an oxygen atom, a sulfur atom, and a nitrogen atom. Of these, a fluorenyl group is preferable.

The aryl group for R³⁴ may have a substituent such as an alkyl group of 1 to 10 carbon atoms, a halogenated alkyl group, or an alkoxy group. The alkyl group and halogenated alkyl group as the substituent preferably has 1 to 8 carbon atoms, and more preferably 1 to 4 carbon atoms. The halogenated alkyl group is preferably a fluorinated alkyl group.

The alkyl group having no substituent or the halogenated alkyl group for R³⁵ preferably has 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, and most preferably 1 to 6 carbon atoms.

As R³⁵, a halogenated alkyl group is preferable, and a partially or completely fluorinated alkyl group is more preferable.

In terms of enhancing the strength of the acid generated, the fluorinated alkyl group for R³⁵ preferably has 50% or more of the hydrogen atoms fluorinated, more preferably 70% or more, still more preferably 90% or more. A completely fluorinated alkyl group in which 100% of the hydrogen atoms are substituted with fluorine atoms is particularly desirable.

In general formula (B-3), the alkyl group having no substituent and the halogenated alkyl group for R³⁶ are the same as the alkyl group having no substituent and the halogenated alkyl group for R³³.

Examples of the divalent or trivalent aromatic hydrocarbon group for R³⁷ include groups in which one or two hydrogen atoms have been removed from the aryl group for R³⁴.

As the alkyl group having no substituent or the halogenated alkyl group for R³⁸, the same one as the alkyl group having no substituent or the halogenated alkyl group for R³⁵ can be used.

p″ is preferably 2.

Specific examples of suitable oxime sulfonate-based acid generators include

-   α-(p-toluenesulfonyloxyimino)-benzyl cyanide, -   α-(p-chlorobenzenesulfonyloxyimino)-benzyl cyanide, -   α-(4-nitrobenzenesulfonyloxyimino)-benzyl cyanide, -   α-(4-nitro-2-trifluoromethylbenzenesulfonyloxyimino)-benzyl cyanide, -   α-(benzenesulfonyloxyimino)-4-chlorobenzyl cyanide, -   α-(benzenesulfonyloxyimino)-2,4-dichlorobenzyl cyanide, -   α-(benzenesulfonyloxyimino)-2,6-dichlorobenzyl cyanide, -   α-(benzenesulfonyloxyimino)-4-methoxybenzyl cyanide, -   α-(2-chlorobenzenesulfonyloxyimino)-4-methoxybenzyl cyanide, -   α-(benzenesulfonyloxyimino)-thien-2-yl acetonitrile, -   α-(4-dodecylbenzenesulfonyloxyimino)benzyl cyanide, -   α-[(p-toluenesulfonyloxyimino)-4-methoxyphenyl]acetonitrile, -   α-[(dodecylbenzenesulfonyloxyimino)-4-methoxyphenyl]acetonitrile, -   α-(tosyloxyimino)-4-thienyl cyanide,     α-(methylsulfonyloxyimino)-1-cyclopentenyl acetonitrile,     α-(methylsulfonyloxyimino)-1-cyclohexenyl acetonitrile, -   α-(methylsulfonyloxyimino)-1-cycloheptenyl acetonitrile, -   α-(methylsulfonyloxyimino)-1-cyclooctenyl acetonitrile, -   α-(trifluoromethylsulfonyloxyimino)-1-cyclopentenyl acetonitrile, -   α-(trifluoromethylsulfonyloxyimino)-cyclohexyl acetonitrile, -   α-(ethylsulfonyloxyimino)-ethyl acetonitrile,     α-(propylsulfonyloxyimino)-propyl acetonitrile,     α-(cyclohexylsulfonyloxyimino)-cyclopentyl acetonitrile, -   α-(cyclohexylsulfonyloxyimino)-cyclohexyl acetonitrile, -   α-(cyclohexylsulfonyloxyimino)-1-cyclopentenyl acetonitrile, -   α-(ethylsulfonyloxyimino)-1-cyclopentenyl acetonitrile, -   α-(isopropylsulfonyloxyimino)-1-cyclopentenyl acetonitrile, -   α-(n-butylsulfonyloxyimino)-1-cyclopentenyl acetonitrile, -   α-(ethylsulfonyloxyimino)-1-cyclohexenyl acetonitrile, -   α-(isopropylsulfonyloxyimino)-1-cyclohexenyl acetonitrile, -   α-(n-butylsulfonyloxyimino)-1-cyclohexenyl acetonitrile, -   α-(methylsulfonyloxyimino)-phenyl acetonitrile, -   α-(methylsulfonyloxyimino)-p-methoxyphenyl acetonitrile, -   α-(trifluoromethylsulfonyloxyimino)-phenyl acetonitrile, -   α-(trifluoromethylsulfonyloxyimino)-p-methoxyphenyl acetonitrile, -   α-(ethylsulfonyloxyimino)-p-methoxyphenyl acetonitrile, -   α-(propylsulfonyloxyimino)-p-methylphenyl acetonitrile, and -   α-(methylsulfonyloxyimino)-p-bromophenyl acetonitrile.

Further, oxime sulfonate-based acid generators disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 9-208554 (Chemical Formulas 18 and 19 shown in paragraphs [0012] to [0014]) and oxime sulfonate-based acid generators disclosed in WO 2004/074242A2 (Examples 1 to 40 described at pages 65 to 85) may be preferably used.

Furthermore, as preferable examples, the following can be mentioned.

Among the above-mentioned compounds, the following 4 compounds are preferable.

Of the aforementioned diazomethane-based acid generators, specific examples of suitable bisalkyl or bisaryl sulfonyl diazomethanes include bis(isopropylsulfonyl)diazomethane, bis(p-toluenesulfonyl)diazomethane, bis(1,1-dimethylethylsulfonyl)diazomethane, bis(cyclohexylsulfonyl)diazomethane, and bis(2,4-dimethylphenylsulfonyl)diazomethane.

Further, diazomethane-based acid generators disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 11-035551, Japanese Unexamined Patent Application, First Publication No. Hei 11-035552 and Japanese Unexamined Patent Application, First Publication No. Hei 11-035573 may be preferably used.

Furthermore, as poly(bis-sulfonyl)diazomethanes, those disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 11-322707, including

-   1,3-bis(phenylsulfonyldiazomethylsulfonyl)propane, -   1,4-bis(phenylsulfonyldiazomethylsulfonyl)butane, -   1,6-bis(phenylsulfonyldiazomethylsulfonyl)hexane, -   1,10-bis(phenylsulfonyldiazomethylsulfonyl)decane, -   1,2-bis(cyclohexylsulfonyldiazomethylsulfonyl)ethane, -   1,3-bis(cyclohexylsulfonyldiazomethylsulfonyl)propane, -   1,6-bis(cyclohexylsulfonyldiazomethylsulfonyl)hexane, and -   1,10-bis(cyclohexylsulfonyldiazomethylsulfonyl)decane, may be     mentioned.

As the component (B), one type of these acid generators may be used alone, or two or more types may be used in combination.

In the present invention, among the above-mentioned examples, as the component (B), it is preferable to use an onium salt having a fluorinated alkylsulfonic acid ion and/or an onium salt having an anion moiety represented by general formula (b-3) above, and it is particularly desirable to use such onium salts in combination.

The amount of the component (B) within the positive resist composition of the present invention is preferably 0.5 to 30 parts by weight, more preferably 1 to 20 parts by weight, and most preferably 2 to 15 parts by weight, relative to 100 parts by weight of the component (A). When the amount of the component (B) is within the above-mentioned range, formation of a resist pattern can be satisfactorily performed. Further, by virtue of the above-mentioned range, a uniform solution can be obtained and the storage stability becomes satisfactory.

<Optional Component>

In the positive resist composition of the present invention, for improving the resist pattern shape and the post exposure stability of the latent image formed by the pattern-wise exposure of the resist layer, a nitrogen-containing organic compound (D) (hereafter referred to as the component (D)) may be added as an optional component.

A multitude of these components (D) have already been proposed, and any of these known compounds may be used, although a cyclic amine, an aliphatic amine, and particularly a secondary aliphatic amine or tertiary aliphatic amine is preferable. Here, an aliphatic amine is an amine having one or more aliphatic groups, and the aliphatic groups preferably have 1 to 12 carbon atoms.

Examples of these aliphatic amines include amines in which at least one hydrogen atom of ammonia (NH₃) has been substituted with an alkyl group or hydroxyalkyl group of no more than 12 carbon atoms (i.e., alkylamines or alkyl alcohol amines), and cyclic amines.

Specific examples of alkylamines and alkylalcoholamines include monoalkylamines such as n-hexylamine, n-heptylamine, n-octylamine, n-nonylamine, and n-decylamine; dialkylamines such as diethylamine, di-n-propylamine, di-n-heptylamine, di-n-octylamine, and dicyclohexylamine; trialkylamines such as trimethylamine, triethylamine, tri-n-propylamine, tri-n-butylamine, tri-n-hexylamine, tri-n-pentylamine, tri-n-heptylamine, tri-n-octylamine, tri-n-nonylamine, tri-n-decanylamine, and tri-n-dodecylamine; and alkyl alcohol amines such as diethanolamine, triethanolamine, diisopropanolamine, triisopropanolamine, di-n-octanolamine, and tri-n-octanolamine. Among these, trialkylamines of 5 to 10 carbon atoms are preferable, and tri-n-pentylamine is particularly desirable.

Examples of the cyclic amine include heterocyclic compounds containing a nitrogen atom as a hetero atom. The heterocyclic compound may be a monocyclic compound (aliphatic monocyclic amine), or a polycyclic compound (aliphatic polycyclic amine).

Specific examples of the aliphatic monocyclic amine include piperidine, and piperazine.

The aliphatic polycyclic amine preferably has 6 to 10 carbon atoms, and specific examples thereof include 1,5-diazabicyclo[4.3.0]-5-nonene, 1,8-diazabicyclo[5.4.0]-7-undecene, hexamethylenetetramine, and 1,4-diazabicyclo[2.2.2]octane.

These compounds can be used either alone, or in combinations of two or more different compounds.

The component (D) is typically used in an amount within a range from 0.01 to 5.0 parts by weight, relative to 100 parts by weight of the component (A).

Furthermore, in the positive resist composition of the present invention, for preventing any deterioration in sensitivity, and improving the resist pattern shape and the post exposure stability of the latent image formed by the pattern-wise exposure of the resist layer, at least one compound (E) (hereafter referred to as the component (E)) selected from the group consisting of an organic carboxylic acid, or a phosphorus oxo acid or derivative thereof can be added as an optional component.

Examples of suitable organic carboxylic acids include acetic acid, malonic acid, citric acid, malic acid, succinic acid, benzoic acid, and salicylic acid. Among these, salicylic acid is particularly preferable.

Examples of phosphorus oxo acids or derivatives thereof include phosphoric acid, phosphonic acid and phosphinic acid. Among these, phosphonic acid is particularly desirable.

Examples of phosphorus oxo acid derivatives include esters in which a hydrogen atom within the above-mentioned oxo acids is substituted with a hydrocarbon group. Examples of the hydrocarbon group include an alkyl group of 1 to 5 carbon atoms and an aryl group of 6 to 15 carbon atoms.

Examples of phosphoric acid derivatives include phosphoric acid esters such as di-n-butyl phosphate and diphenyl phosphate.

Examples of phosphonic acid derivatives include phosphonic acid esters such as dimethyl phosphonate, di-n-butyl phosphonate, phenylphosphonic acid, diphenyl phosphonate and dibenzyl phosphonate.

Examples of phosphinic acid derivatives include phosphinic acid esters such as phenylphosphinic acid.

Of these, one type may be used alone, or two or more types may be used in combination.

As the component (E), an organic carboxylic acid is preferable, and salicylic acid is particularly desirable.

The component (E) is typically used in an amount within a range from 0.01 to 5.0 parts by weight, relative to 100 parts by weight of the component (A).

If desired, other miscible additives can also be added to the positive resist composition of the present invention. Examples of such miscible additives include additive resins for improving the performance of the resist film, surfactants for improving the applicability, dissolution inhibitors, plasticizers, stabilizers, colorants, halation prevention agents, and dyes.

The positive resist composition of the present invention can be prepared by dissolving the materials for the resist composition in an organic solvent (hereafter, frequently referred to as “component (S)”).

The component (S) may be any organic solvent which can dissolve the respective components to give a uniform solution, and any one or more kinds of organic solvents can be appropriately selected from those which have been conventionally known as solvents for a chemically amplified resist.

Examples thereof include lactones such as γ-butyrolactone; ketones such as acetone, methyl ethyl ketone, cyclohexanone, methyl-n-amyl ketone, methyl isoamyl ketone, and 2-heptanone; polyhydric alcohols, such as ethylene glycol, diethylene glycol, propylene glycol and dipropylene glycol; compounds having an ester bond, such as ethylene glycol monoacetate, diethylene glycol monoacetate, propylene glycol monoacetate, and dipropylene glycol monoacetate; polyhydric alcohol derivatives including compounds having an ether bond, such as a monoalkylether (e.g., monomethylether, monoethylether, monopropylether or monobutylether) or monophenylether of any of these polyhydric alcohols or compounds having an ester bond (among these, propylene glycol monomethyl ether acetate (PGMEA) and propylene glycol monomethyl ether (PGME) are preferable); cyclic ethers such as dioxane; esters such as methyl lactate, ethyl lactate (EL), methyl acetate, ethyl acetate, butyl acetate, methyl pyruvate, ethyl pyruvate, methyl methoxypropionate, and ethyl ethoxypropionate; and aromatic organic solvents such as anisole, ethylbenzylether, cresylmethylether, diphenylether, dibenzylether, phenetole, butylphenylether, ethylbenzene, diethylbenzene, amylbenzene, isopropylbenzene, toluene, xylene, cymene and mesitylene.

These solvents can be used individually, or in combination as a mixed solvent.

Among these, propylene glycol monomethyl ether acetate (PGMEA), propylene glycol monomethyl ether (PGME) and ethyl lactate (EL) are preferable.

Further, among the mixed solvents, a mixed solvent obtained by mixing PGMEA with a polar solvent is preferable. The mixing ratio (weight ratio) of the mixed solvent can be appropriately determined, taking into consideration the compatibility of the PGMEA with the polar solvent, but is preferably in the range of 1:9 to 9:1, more preferably from 2:8 to 8:2.

Specifically, when EL is mixed as the polar solvent, the PGMEA:EL weight ratio is preferably from 1:9 to 9:1, and more preferably from 2:8 to 8:2. Alternatively, when PGME is mixed as the polar solvent, the PGMEA:PGME weight ratio is preferably from 1:9 to 9:1, more preferably from 2:8 to 8:2, and still more preferably 3:7 to 7:3.

Further, as the component (S), a mixed solvent of at least one of PGMEA and EL with γ-butyrolactone is also preferable. The mixing ratio (former:latter) of such a mixed solvent is preferably from 70:30 to 95:5.

The amount of the component (S) used is not particularly limited, and is appropriately adjusted to a concentration which enables coating of a coating solution to a substrate, depending on the thickness of the coating film. In general, the component (S) is used in an amount such that the solid content of the resist composition is within the range from 2 to 20% by weight, and preferably from 3 to 15% by weight.

<<Method of Forming a Resist Pattern>>

The method of forming a resist pattern according to the present invention includes: applying a positive resist composition of the present invention to a substrate to form a resist film on the substrate; subjecting the resist film to exposure; and developing the resist film to form a resist pattern.

More specifically, the method for forming a resist pattern according to the present invention can be performed, for example, as follows. Firstly, the resist composition is applied onto a substrate such as a silicon wafer using a spinner or the like, and a prebake (post applied bake (PAB)) is conducted at 80 to 150° C. for 40 to 120 seconds, preferably 60 to 90 seconds to form a resist film. Then, for example, using an ArF exposure apparatus or the like, the resist film is selectively exposed to an ArF excimer laser beam through a desired mask pattern, followed by post exposure bake (PEB) at 80 to 150° C. for 40 to 120 seconds, preferably 60 to 90 seconds. Subsequently, developing is conducted using an alkali developing solution such as a 0.1 to 10% by weight aqueous solution of tetramethylammonium hydroxide. In this manner, a resist pattern that is faithful to the mask pattern can be obtained.

An organic or inorganic antireflection film may be provided between the substrate and the applied coating layer of the positive resist composition.

The wavelength to be used for exposure is not particularly limited and the exposure can be conducted using radiations such as ArF excimer laser, KrF excimer laser, F₂ excimer laser, extreme ultraviolet rays (EUV), vacuum ultraviolet rays (VUV), electron beam (EB), X-rays, and soft X-rays. The positive resist composition of the present invention is particularly effective to ArF excimer laser.

The positive resist composition and method of forming a resist pattern according to the present invention is capable of achieving excellent solubility in an organic solvent.

Further, according to the present invention, a resist pattern having an excellent shape can be formed. For example, a resist pattern in which the cross-sectional shape exhibits a high rectangularity, i.e., the perpendicularity of the side walls of the pattern is high, surface roughness is small, and the like. Furthermore, when a resist pattern is formed as a hole pattern, no distortion of the pattern is observed as viewed from the upper side of the pattern, and a hole pattern having excellent circularity can be formed.

Moreover, according to the present invention, an excellent PEB margin can be achieved. For example, even when the PEB temperature varies during PEB, a resist pattern can be formed with small variation in size.

The reasons why these effects can be achieved are presumed as follows.

Conventionally, in a positive resist composition used for ArF excimer laser lithography and the like, for the purpose of enhancing the compatibility with the developing solution, improving the alkali solubility of the exposed portions, and increasing the difference in the alkali solubility between exposed portions and unexposed portions (dissolution contrast), a resin containing a polar group-containing aliphatic hydrocarbon group, e.g., a structural unit having the structure “-(aliphatic cyclic group)-OH”, or a structural unit containing a bulky tertiary alkyl ester-type acid dissociable, dissolution inhibiting group such as a 2-alkyl-2-adamantyl group, have been used.

However, such a resin containing a structural unit having the structure “-(aliphatic cyclic group)-OH” reduces the solubility of the resin in an organic solvent by its high hydrophilicity, and thus, the solubility of a positive resist composition containing such a resin in an organic solvent becomes poor.

In contrast, the component (A) used in the present invention contains a polymer (A1) including a structural unit (a0) having the structure “—Y¹—(CH₂)_(e)—O—Z”. In this structure “—Y¹—(CH₂)_(e)—O—Z”, Z exhibits low polarity as compared to a hydrogen atom. Further, the molecular chain of this structure is relatively long. Therefore, it is presumed that the compatibility of the polymer (A1) for an organic solvent is enhanced, and as a result, the solubility of the entire component (A) in an organic solvent is improved.

Furthermore, by using the polymer (A1) in combination with the polymer (A2) having an acetal-type acid dissociable, dissolution inhibiting group, it is presumed that some sort of interaction occurs between the polymer (A1) and the polymer (A2), and the pattern shape and the PEB margin are improved.

The effect of improvement in the pattern shape and the PEB margin is significant especially when a resist pattern is formed as a hole pattern.

In addition, the following is noted. Conventionally, in the fields of lithography, a problem arises in that defects are generated on the surface of the formed resist pattern. However, according to the present invention, such defects can be reduced.

“Defects” refers to general abnormalities of a resist pattern, which are detected when observed from directly above the developed resist pattern, using, for example, surface defect detection equipment (trade name: “KLA”) manufactured by KLA-TENCOR CORPORATION. Examples of these abnormalities include post-developing scum, foam, dust, bridges across different portions of the resist pattern, color irregularities, and foreign deposits. Improvements in the defect problem are becoming more and more important as the demand for resist patterns with higher resolution is increasing. Especially, in lithography techniques using ArF excimer lasers and lithography techniques developed thereafter such as lithography techniques using F₂ excimer lasers, EUV, electron beam (EB) and the like as the light source, when a fine pattern such as a resist pattern of no more than 130 nm is formed, these defects are becoming of serious problems.

One of the reasons for defects is presumed to be the poor solubility in an organic solvent and the low stability of the resist solution due to such poor solubility. The positive resist composition of the present invention exhibits excellent solubility in an organic solvent, and is therefore effective in solving the problems of defects.

Moreover, in the present invention, the structural unit (a0) and the structural unit (a1) are included in separate polymers (i.e., the polymer (A1) and the polymer (A2)). Therefore, by adjusting the mixing ratio or the like of the polymer (A1) to the polymer (A2), the amounts of the structural units (a0) and (a1) within the entire component (A) can be easily adjusted, so that the solubility of the component (A) in an organic solvent and various lithography properties such as PEB margin and the like can be easily adjusted. Further, the polymer (A1) and the polymer (A2) can be easily synthesized.

EXAMPLES

As follows is a description of examples of the present invention, although the scope of the present invention is by no way limited by these examples.

Resins (A)-1 to (A)-3 used in Example 1 and Comparative Example 1 were synthesized in Synthesis Examples 2 to 4 by copolymerizing monomers (1) to (9) shown below (the production method of monomer (1) is shown below) by a conventional dropwise polymerization method.

In Synthesis Examples 2 to 4, Mw and Mw/Mn of resins (A)-1 to (A)-3 were measured by GPC.

In Synthesis Examples 2 to 4, each of the subscript numerals at the lower right of the brackets in formulas (A)-1 to (A)-3 indicate the amount (mol %) of the respective structural units.

Synthesis Example 1 [Synthesis of Monomer (1)]

150 mL of THF (tetrahydrofuran) were charged into an eggplant-shaped flask, and 20 g of the monomer (8) above (1-(3-hydroxyadamantane) methacrylate) and 10 g of triethylamine were added thereto. Then, 22 g of t-butoxycarboxylic acid anhydride were added while cooling with ice, and the resultant was stirred at room temperature for 3 hours. Thereafter, the reaction liquid was subjected to extraction with ethyl acetate, followed by concentration, thereby obtaining the monomer (1) above.

Synthesis Example 2

85 g of PGMEA was charged into a flask equipped with an inlet for nitrogen, a stirrer, a condenser and a thermometer in a nitrogen atmosphere, and the temperature of the water bath was elevated to 80° C. while stirring.

A monomer solution obtained by mixing 32.4 g of monomer (1), 34.8 g of monomer (2), 32.8 g of monomer (5), 154 g of PGMEA and 2.8 g of 2,2′-azobisisobutyronitrile (AIBN) were added dropwise into the flask using a dripping apparatus at a constant rate over 6 hours, and then the temperature was maintained at 80° C. for 1 hour. Then, the temperature of the reaction liquid was cooled to room temperature. Subsequently, the resulting reaction liquid was added dropwise to methanol about 30 times in amount while stirring, to obtain a colorless precipitate. The obtained precipitate was subjected to filtration, and then the precipitate was washed in methanol in an amount about 30 times the amount of the monomers used in the polymerization. The resulting precipitate was subjected to filtration, followed by drying at 50° C. under reduced pressure for about 40 hours, thereby obtaining a resin (A)-1. The obtained resin (A)-1 was subjected to GPC measurement. As a result, it was found that the weight average molecular weight (Mw) was 10,000, and the dispersity (Mw/Mn) was 1.7.

Synthesis Example 3

85 g of PGMEA was charged into a flask equipped with an inlet for nitrogen, a stirrer, a condenser and a thermometer in a nitrogen atmosphere, and the temperature of the water bath was elevated to 80° C. while stirring.

A monomer solution obtained by mixing 47.7 g of monomer (3), 29.8 g of monomer (6), 22.5 g of monomer (8), 154 g of PGMEA and 2.7 g of 2,2′-azobisisobutyronitrile (AIBN) were added dropwise into the flask using a dripping apparatus at a constant rate over 6 hours, and then the temperature was maintained at 80° C. for 1 hour. Then, the temperature of the reaction liquid was cooled to room temperature. Subsequently, the resulting reaction liquid was added dropwise to methanol about 30 times in amount while stirring, to obtain a colorless precipitate. The obtained precipitate was subjected to filtration, and then the precipitate was washed in methanol in an amount about 30 times the amount of the monomers used in the polymerization. The resulting precipitate was subjected to filtration, followed by drying at 50° C. under reduced pressure for about 40 hours, thereby obtaining a resin (A)-2.

The obtained resin (A)-2 was subjected to GPC measurement. As a result, it was found that the weight average molecular weight (Mw) was 7,000, and the dispersity (Mw/Mn) was 2.0.

Synthesis Example 4

85 g of PGMEA was charged into a flask equipped with an inlet for nitrogen, a stirrer, a condenser and a thermometer in a nitrogen atmosphere, and the temperature of the water bath was elevated to 80° C. while stirring.

A monomer solution obtained by mixing 43.7 g of monomer (4), 36.7 g of monomer (7), 19.6 g of monomer (9), 154 g of PGMEA and 2.5 g of 2,2′-azobisisobutyronitrile (AIBN) were added dropwise into the flask using a dripping apparatus at a constant rate over 6 hours, and then the temperature was maintained at 80° C. for 1 hour. Then, the temperature of the reaction liquid was cooled to room temperature. Subsequently, the resulting reaction liquid was added dropwise to methanol about 30 times in amount while stirring, to obtain a colorless precipitate. The obtained precipitate was subjected to filtration, and then the precipitate was washed in methanol in an amount about 30 times the amount of the monomers used in the polymerization. The resulting precipitate was subjected to filtration, followed by drying at 50° C. under reduced pressure for about 40 hours, thereby obtaining a resin (A)-3. The obtained resin (A)-3 was subjected to GPC measurement. As a result, it was found that the weight average molecular weight (Mw) was 10,000, and the dispersity (Mw/Mn) was 2.0.

Example 1, Comparative Example 1

The components shown in Table 1 were mixed together and dissolved to obtain positive resist compositions.

TABLE 1 Component Component Component Component Component (A) (B) (D) (E) (S) Ex. 1 (A)-1 (A)-2 (B)-1 (B)-2 (D)-1 (E)-1 (S)-1 [40] [60] [3.0] [0.8] [0.5] [0.2] [1500] Comp. Ex. 1 (A)-3 (B)-1 (B)-2 (D)-1 (E)-1 (S)-1 [100] [3.0] [0.8] [0.2] [0.2] [1500]

In Table 1, the reference characters indicate the following. Further, the values in brackets [ ] indicate the amount (in terms of parts by weight) of the component added.

-   (B)-1: a compound represented by formula (B)-1 shown below -   (B)-2: a compound represented by formula (B)-2 shown below -   (D)-1: tri-n-pentylamine -   (E)-1: salicylic acid -   (S)-1: a mixed solvent of PGMEA/PGME=6/4 (weight ratio)

With respect to each of the positive resist compositions, a resist pattern was formed in the following manner, and lithography properties were evaluated.

<Evaluation of Resolution>

An organic anti-reflection film composition (product name: ARC29A, manufactured by Brewer Science Ltd.) was applied onto an 8-inch silicon wafer using a spinner, and the composition was then baked at 205° C. for 60 seconds, thereby forming an organic anti-reflection film having a film thickness of 77 nm. Then, a positive resist composition was applied onto the anti-reflection film using a spinner, and was then prebaked (PAB) on a hotplate at a temperature indicated in Table 2 for 60 seconds and dried, thereby forming a resist film having a film thickness of 180 nm.

Subsequently, the resist film was selectively irradiated with an ArF excimer laser (193 nm) through a mask pattern (6% half tone rectile), using an ArF exposure apparatus NSR-S-302 (manufactured by Nikon Corporation, NA (numerical aperture)=0.60, σ=0.75).

Thereafter, a PEB treatment was conducted at the temperature indicated in Table 2 for 60 seconds, followed by development for 30 seconds at 23° C. in a 2.38% by weight aqueous solution of tetramethylammonium hydroxide (TMAH). Then, the resist was washed for 30 seconds with pure water, followed by drying by shaking.

For increasing the reliability of the evaluations of the pattern shape, PEB margin and the like, the amount of (D)-1 in Comparative Example 1 was lessened from the amount of (D)-1 in Example 1, so as to make the exposure dose (sensitivity) the same.

As a result, in each of the examples, a contact hole pattern (hereafter, referred to as “Dence CH pattern”) having a hole diameter of 140 nm and a pitch of 280 nm, and a CH pattern (hereafter, referred to as “Iso CH pattern”) having a hole diameter of 140 nm and a pitch of 840 nm were formed. (The exposure does (unit: mJ/cm² (amount of energy per unit area)) with which a pattern was formed was determined as the Eop.)

TABLE 2 Comparative Example 1 Example 1 PAB temperature/PEB 95/95 95/98 95/100 110/90 temperature (° C.) Eop Dence 37 35 35 42 (mJ/cm²) CH pattern Iso 40 39 38 49 CH pattern

<Evaluation of PEB Margin>

With respect to the Dence CH patterns and Iso CH patterns obtained using the positive resist composition of Example 1, the size (hole diameter; unit: nm) of each of the resist patterns obtained with PEB temperatures of 95° C., 98° C. and 100° C. was measured. Then, a graph was obtained by plotting the size of the resist pattern on the vertical axis and the PEB temperature on the horizontal axis, and the gradient of the graph, i.e., the change in the size of the resist pattern per change of 1° C. in the PEB temperature was determined.

As a result, it was found that the change in the size of the Dence CH pattern of Example 1 was 4 nm/° C., and the change in the size of the Iso CH pattern was 2 nm/° C.

With respect to the positive resist composition of Comparative Example 1, Dence CH patterns and Iso CH patterns were formed in the same manner as described above, except that the PEB temperatures were changed to 90° C., 92° C. and 95° C., and the change in the size of the resist pattern was determined. As a result, it was found that in Comparative Example 1, the change in the size of the resist pattern exceeded 10 nm/° C. for both of the Dence CH pattern and the Iso CH pattern.

The smaller the value of the change in the size, the smaller the change in the pattern size depending on the variation in the PEB temperature, indicating that the PEB margin is excellent.

As seen from the results above, the positive resist composition of Example 1 in which a combination of (A)-1 corresponding to the polymer (A1) and (A)-2 corresponding to the polymer (A2) was used as the component (A) exhibited an excellent PEB margin.

On the other hand, the positive resist composition of Comparative Example 1 having the same formulation as that of a resin conventionally used for forming a CH pattern exhibited an extremely poor PEB margin.

<Evaluation of the Shape>

With respect to the Dence CH patterns and Iso patterns formed in the evaluation of resolution, the shape of the upper portion and the cross-sectional shape were observed using a measuring SEM (product name: S-9220, manufactured by Hitachi, Ltd.).

As a result, with respect to the patterns formed using the positive resist composition of Example 1, in each of the example of various PEB temperatures, it was found that the shape of the holes as viewed from the upper side of the patterns exhibited a high circularity. Further, with respect to the cross-sectional shape, it was found that the perpendicularity of the side walls of the pattern was high, and the pattern exhibited an excellent rectangularity.

On the other hand, with respect to the patterns formed using the positive resist composition of Comparative Example 1, distortion was observed on the periphery of the holes as viewed from the upper side of the patterns, and the cross-sectional shape was tapered.

<<Evaluation of Solubility in an Organic Solvent>>

With respect to the components (A) used in Example 1 and Comparative Example 1 (a mixture of (A)-1/(A)-2=60/40 (weight ratio) and (A)-3 alone), the solubility in an organic solvent was evaluated as follows.

Using a mixed solvent of PGMEA/PGME=6/4 (weight ratio) as an organic solvent, each of the components (A) used in Example 1 and Comparative Example 1 was added in an amount of 1 g to 12 g of the mixed solvent (23° C.).

As a result, the component (A) used in Example 1 was completely dissolved after about 15 minutes by stirring while subjecting to an ultrasonic wave treatment.

On the other hand, the component (A) used in Comparative Example 1 required about 30 minutes to be completely dissolved by stirring while subjecting to an ultrasonic wave treatment.

As seen from the results above, with respect to the positive resist composition of Example 1 which was a positive resist composition according to the present invention, the solubility of the component (A) used in an organic solvent was extremely high, and the shape of the resist pattern formed and the PEB margin were excellent.

INDUSTRIAL APPLICABILITY

The positive resist composition of the present invention exhibits an excellent solubility in an organic solvent, and hence, defects can be improved. Further, the positive resist composition of the present invention is capable of forming a resist pattern which exhibits an excellent shape and an excellent PEB margin. Therefore, the present invention is extremely useful in industry. 

1. A positive resist composition comprising a resin component (A) which exhibits increased alkali solubility under action of acid and an acid-generator component (B) which generates acid upon exposure, said resin component (A) comprising: a polymer (A1) comprising a structural unit (a0) represented by general formula (a0) shown below and no structural unit (a1) derived from an acrylate ester containing an acetal-type acid dissociable, dissolution inhibiting group, exclusive of said structural unit (a0), and a polymer (A2) comprising said structural unit (a1) and no structural unit (a0):

wherein R represents a hydrogen atom, a halogen atom, a lower alkyl group or a halogenated lower alkyl group; Y¹ represents an aliphatic cyclic group; Z represents a tertiary alkyloxycarbonyl group, a tertiary alkyloxycarbonylalkyl group or an alkoxyalkyl group; a represents an integer of 1 to 3, and b represents an integer of 0 to 2, with the proviso that a+b=1 to 3; and each of c, d and e independently represents an integer of 0 to
 3. 2. The positive resist composition according to claim 1, wherein the amount of said structural unit (a0) within said polymer (A1), based on the combined total of all structural units constituting said polymer (A1) is 1 to 40 mol %.
 3. The positive resist composition according to claim 1, wherein said polymer (A1) further comprises a structural unit (a1′) derived from an acrylate ester having a tertiary alkyl ester-type acid dissociable, dissolution inhibiting group.
 4. The positive resist composition according to claim 1, wherein at least one of said polymer (A1) and said polymer (A2) further comprises a structural unit (a2) derived from an acrylate ester containing a lactone-containing cyclic group.
 5. The positive resist composition according to claim 1, wherein said polymer (A2) further comprises a structural unit (a3) derived from an acrylate ester containing a polar group-containing aliphatic hydrocarbon group.
 6. The positive resist composition according to claim 1, which further comprises a nitrogen-containing organic compound (D).
 7. A method of forming a resist pattern, comprising: applying a positive resist composition of any one of claims 1 to 6 to a substrate to form a resist film on the substrate; conducting exposure of said resist film; and developing said resist film to form a resist pattern.
 8. The positive resist composition according to claim 1, wherein Z represents a group represented by general formula (II) shown below, a group represented by general formula (III) shown below or an alkoxyalkyl group:

wherein each of R²¹ to R²³ independently represents a linear or branched alkyl group.
 9. The positive resist composition according to claim 1, wherein Z represents a tertiary alkyloxycarbonyl group or a tertiary alkyloxycarbonylalkyl group.
 10. The positive resist composition according to claim 1, wherein Z represents a group represented by general formula (II) shown below or a group represented by general formula (III) shown below:

wherein each of R²¹ to R²³ independently represents a linear or branched alkyl group. 